Pair of Linear Equations in Two Variables | Exercise 3.1

Question 3

  1. On comparing the ratios a1a2\frac{a_1}{a_2}, b1b2\frac{b_1}{b_2} and c1c2\frac{c_1}{c_2}, find out whether the following pair of linear equations are consistent, or inconsistent.

(i) 3x+2y=53x + 2y = 5; 2x3y=72x - 3y = 7

(ii) 2x3y=82x - 3y = 8; 4x6y=94x - 6y = 9

(iii) 32x+53y=7\frac{3}{2}x + \frac{5}{3}y = 7; 9x10y=149x - 10y = 14

(iv) 5x3y=115x - 3y = 11; 10x+6y=22-10x + 6y = -22

(v) 43x+2y=8\frac{4}{3}x + 2y = 8; 2x+3y=122x + 3y = 12

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Solution

We compare the ratios of coefficients to determine consistency.

Step 1 — Analyze Part (i)

Let's write the equations in standard form. The first equation is 3x+2y5=03x + 2y - 5 = 0. The second equation is 2x3y7=02x - 3y - 7 = 0. We identify the coefficients. a1=3a_1 = \mathbf{3}, b1=2b_1 = \mathbf{2}, c1=5c_1 = \mathbf{-5}. a2=2a_2 = \mathbf{2}, b2=3b_2 = \mathbf{-3}, c2=7c_2 = \mathbf{-7}.

Now, we calculate the ratios. a1a2=32\frac{a_1}{a_2} = \frac{3}{2}

b1b2=23\frac{b_1}{b_2} = \frac{2}{-3}

We compare these two ratios. 3223\frac{3}{2} \neq \frac{2}{-3} This means a1a2b1b2\frac{a_1}{a_2} \neq \frac{b_1}{b_2}. The lines intersect at one point.

Consistent\boxed{\text{Consistent}}

Step 2 — Analyze Part (ii)

Let's write the equations in standard form. The first equation is 2x3y8=02x - 3y - 8 = 0. The second equation is 4x6y9=04x - 6y - 9 = 0. We identify the coefficients. a1=2a_1 = \mathbf{2}, b1=3b_1 = \mathbf{-3}, c1=8c_1 = \mathbf{-8}. a2=4a_2 = \mathbf{4}, b2=6b_2 = \mathbf{-6}, c2=9c_2 = \mathbf{-9}.

Now, we calculate the ratios. a1a2=24=12\frac{a_1}{a_2} = \frac{2}{4} = \frac{1}{2}

b1b2=36=12\frac{b_1}{b_2} = \frac{-3}{-6} = \frac{1}{2} The first two ratios are equal. So, we calculate the third ratio. c1c2=89=89\frac{c_1}{c_2} = \frac{-8}{-9} = \frac{8}{9} Now, we compare all three ratios. 12=1289\frac{1}{2} = \frac{1}{2} \neq \frac{8}{9} This means a1a2=b1b2c1c2\frac{a_1}{a_2} = \frac{b_1}{b_2} \neq \frac{c_1}{c_2}. The lines are parallel and do not intersect.

Inconsistent\boxed{\text{Inconsistent}}

Step 3 — Analyze Part (iii)

Let's write the equations in standard form. The first equation is 32x+53y7=0\frac{3}{2}x + \frac{5}{3}y - 7 = 0. The second equation is 9x10y14=09x - 10y - 14 = 0. We identify the coefficients. a1=32a_1 = \mathbf{\frac{3}{2}}, b1=53b_1 = \mathbf{\frac{5}{3}}, c1=7c_1 = \mathbf{-7}. a2=9a_2 = \mathbf{9}, b2=10b_2 = \mathbf{-10}, c2=14c_2 = \mathbf{-14}.

Now, we calculate the ratios. a1a2=3/29=318=16\frac{a_1}{a_2} = \frac{3/2}{9} = \frac{3}{18} = \frac{1}{6}

b1b2=5/310=530=16\frac{b_1}{b_2} = \frac{5/3}{-10} = \frac{5}{-30} = -\frac{1}{6}

We compare these two ratios. 1616\frac{1}{6} \neq -\frac{1}{6} This means a1a2b1b2\frac{a_1}{a_2} \neq \frac{b_1}{b_2}. The lines intersect at one point.

Consistent\boxed{\text{Consistent}}

Step 4 — Analyze Part (iv)

Let's write the equations in standard form. The first equation is 5x3y11=05x - 3y - 11 = 0. The second equation is 10x+6y+22=0-10x + 6y + 22 = 0. We identify the coefficients. a1=5a_1 = \mathbf{5}, b1=3b_1 = \mathbf{-3}, c1=11c_1 = \mathbf{-11}. a2=10a_2 = \mathbf{-10}, b2=6b_2 = \mathbf{6}, c2=22c_2 = \mathbf{22}.

Now, we calculate the ratios. a1a2=510=12\frac{a_1}{a_2} = \frac{5}{-10} = -\frac{1}{2}

b1b2=36=12\frac{b_1}{b_2} = \frac{-3}{6} = -\frac{1}{2} The first two ratios are equal. So, we calculate the third ratio. c1c2=1122=12\frac{c_1}{c_2} = \frac{-11}{22} = -\frac{1}{2} Now, we compare all three ratios. 12=12=12-\frac{1}{2} = -\frac{1}{2} = -\frac{1}{2} This means a1a2=b1b2=c1c2\frac{a_1}{a_2} = \frac{b_1}{b_2} = \frac{c_1}{c_2}. The lines are coincident and have many solutions.

Consistent\boxed{\text{Consistent}}

Step 5 — Analyze Part (v)

Let's write the equations in standard form. The first equation is 43x+2y8=0\frac{4}{3}x + 2y - 8 = 0. The second equation is 2x+3y12=02x + 3y - 12 = 0. We identify the coefficients. a1=43a_1 = \mathbf{\frac{4}{3}}, b1=2b_1 = \mathbf{2}, c1=8c_1 = \mathbf{-8}. a2=2a_2 = \mathbf{2}, b2=3b_2 = \mathbf{3}, c2=12c_2 = \mathbf{-12}.

Now, we calculate the ratios. a1a2=4/32=46=23\frac{a_1}{a_2} = \frac{4/3}{2} = \frac{4}{6} = \frac{2}{3}

b1b2=23\frac{b_1}{b_2} = \frac{2}{3} The first two ratios are equal. So, we calculate the third ratio. c1c2=812=23\frac{c_1}{c_2} = \frac{-8}{-12} = \frac{2}{3} Now, we compare all three ratios. 23=23=23\frac{2}{3} = \frac{2}{3} = \frac{2}{3} This means a1a2=b1b2=c1c2\frac{a_1}{a_2} = \frac{b_1}{b_2} = \frac{c_1}{c_2}. The lines are coincident and have many solutions.

Consistent\boxed{\text{Consistent}}

Answer

(i) Consistent (ii) Inconsistent (iii) Consistent (iv) Consistent (v) Consistent

More questions in Exercise 3.1

Q1

Form the pair of linear equations in the following problems, and find their solutions graphically.

(i) 10 students of Class X took part in a Mathematics quiz. If the number of girls is 4 more than the number of boys, find the number of boys and girls who took part in the quiz.

(ii) 5 pencils and 7 pens together cost ₹ 50, whereas 7 pencils and 5 pens together cost ₹ 46. Find the cost of one pencil and that of one pen.

Q2
  1. On comparing the ratios a1a2\frac{a_1}{a_2}, b1b2\frac{b_1}{b_2} and c1c2\frac{c_1}{c_2}, find out whether the lines representing the following pairs of linear equations intersect at a point, are parallel or coincident:

(i) 5x4y+8=05x - 4y + 8 = 0 7x+6y9=07x + 6y - 9 = 0

(ii) 9x+3y+12=09x + 3y + 12 = 0 18x+6y+24=018x + 6y + 24 = 0

(iii) 6x3y+10=06x - 3y + 10 = 0 2xy+9=02x - y + 9 = 0

Q3
  1. On comparing the ratios a1a2\frac{a_1}{a_2}, b1b2\frac{b_1}{b_2} and c1c2\frac{c_1}{c_2}, find out whether the following pair of linear equations are consistent, or inconsistent.

(i) 3x+2y=53x + 2y = 5; 2x3y=72x - 3y = 7

(ii) 2x3y=82x - 3y = 8; 4x6y=94x - 6y = 9

(iii) 32x+53y=7\frac{3}{2}x + \frac{5}{3}y = 7; 9x10y=149x - 10y = 14

(iv) 5x3y=115x - 3y = 11; 10x+6y=22-10x + 6y = -22

(v) 43x+2y=8\frac{4}{3}x + 2y = 8; 2x+3y=122x + 3y = 12

Q4
  1. Which of the following pairs of linear equations are consistent/inconsistent? If consistent, obtain the solution graphically:

(i) x+y=5x + y = 5, 2x+2y=102x + 2y = 10

(ii) xy=8x - y = 8, 3x3y=163x - 3y = 16

(iii) 2x+y6=02x + y - 6 = 0, 4x2y4=04x - 2y - 4 = 0

(iv) 2x2y2=02x - 2y - 2 = 0, 4x4y5=04x - 4y - 5 = 0

Q5
  1. Half the perimeter of a rectangular garden, whose length is 4 m4\text{ m} more than its width, is 36 m36\text{ m}. Find the dimensions of the garden.
Q6
  1. Given the linear equation 2x+3y8=02x + 3y - 8 = 0, write another linear equation in two variables such that the geometrical representation of the pair so formed is:

(i) intersecting lines

(ii) parallel lines

(iii) coincident lines

Q7
  1. Draw the graphs of the equations xy+1=0x - y + 1 = 0 and 3x+2y12=03x + 2y - 12 = 0. Determine the coordinates of the vertices of the triangle formed by these lines and the xx-axis, and shade the triangular region.
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