Exploring Algebraic Identities | Exercise 4.2

Question 1

Factor completely:

(i) 9x2+24xy+16y29x^2 + 24xy + 16y^2

(ii) 4s2+20st+25t24s^2 + 20st + 25t^2

(iii) 49x2+28xy+4y249x^2 + 28xy + 4y^2

(iv) 64p2+323pq+49q264p^2 + \frac{32}{3}pq + \frac{4}{9}q^2

*(v) 3a2+4ab+43b23a^2 + 4ab + \frac{4}{3}b^2

*(vi) 95s2+6sv+5v2\frac{9}{5}s^2 + 6sv + 5v^2

(Hint: 2 was taken out as a common factor in Example 7. Is it possible to do something similar in Exercises (v) and (vi) above?)

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Solution

We will use the algebraic identity for a perfect square trinomial.

Step 1 — Factor 9x2+24xy+16y29x^2 + 24xy + 16y^2

Let's look at the first term. We see that 9x29x^2 is the square of 3x3x. The last term is 16y216y^2. This is the square of 4y4y. Now, let's check the middle term. It should be twice the product of 3x3x and 4y4y. 2×(3x)×(4y)=24xy2 \times (3x) \times (4y) = 24xy. This matches our middle term. So, this is a perfect square trinomial. We use the identity (a+b)2=a2+2ab+b2(a+b)^2 = a^2 + 2ab + b^2.

9x2+24xy+16y2=(3x)2+2(3x)(4y)+(4y)29x^2 + 24xy + 16y^2 = (3x)^2 + 2(3x)(4y) + (4y)^2

=(3x+4y)2= (3x + 4y)^2

(3x+4y)2\boxed{(3x + 4y)^2}

Step 2 — Factor 4s2+20st+25t24s^2 + 20st + 25t^2

Let's examine the first term. We see that 4s24s^2 is the square of 2s2s. The last term is 25t225t^2. This is the square of 5t5t. Now, let's check the middle term. It should be twice the product of 2s2s and 5t5t. 2×(2s)×(5t)=20st2 \times (2s) \times (5t) = 20st. This matches our middle term. So, this is a perfect square trinomial. We use the identity (a+b)2=a2+2ab+b2(a+b)^2 = a^2 + 2ab + b^2.

4s2+20st+25t2=(2s)2+2(2s)(5t)+(5t)24s^2 + 20st + 25t^2 = (2s)^2 + 2(2s)(5t) + (5t)^2

=(2s+5t)2= (2s + 5t)^2

(2s+5t)2\boxed{(2s + 5t)^2}

Step 3 — Factor 49x2+28xy+4y249x^2 + 28xy + 4y^2

Let's look at the first term. We see that 49x249x^2 is the square of 7x7x. The last term is 4y24y^2. This is the square of 2y2y. Now, let's check the middle term. It should be twice the product of 7x7x and 2y2y. 2×(7x)×(2y)=28xy2 \times (7x) \times (2y) = 28xy. This matches our middle term. So, this is a perfect square trinomial. We use the identity (a+b)2=a2+2ab+b2(a+b)^2 = a^2 + 2ab + b^2.

49x2+28xy+4y2=(7x)2+2(7x)(2y)+(2y)249x^2 + 28xy + 4y^2 = (7x)^2 + 2(7x)(2y) + (2y)^2

=(7x+2y)2= (7x + 2y)^2

(7x+2y)2\boxed{(7x + 2y)^2}

Step 4 — Factor 64p2+323pq+49q264p^2 + \frac{32}{3}pq + \frac{4}{9}q^2

Let's examine the first term. We see that 64p264p^2 is the square of 8p8p. The last term is 49q2\frac{4}{9}q^2. This is the square of 23q\frac{2}{3}q. Now, let's check the middle term. It should be twice the product of 8p8p and 23q\frac{2}{3}q. 2×(8p)×(23q)=323pq2 \times (8p) \times \left(\frac{2}{3}q\right) = \frac{32}{3}pq. This matches our middle term. So, this is a perfect square trinomial. We use the identity (a+b)2=a2+2ab+b2(a+b)^2 = a^2 + 2ab + b^2.

64p2+323pq+49q2=(8p)2+2(8p)(23q)+(23q)264p^2 + \frac{32}{3}pq + \frac{4}{9}q^2 = (8p)^2 + 2(8p)\left(\frac{2}{3}q\right) + \left(\frac{2}{3}q\right)^2

=(8p+23q)2= \left(8p + \frac{2}{3}q\right)^2

(8p+23q)2\boxed{\left(8p + \frac{2}{3}q\right)^2}

Step 5 — Factor 3a2+4ab+43b23a^2 + 4ab + \frac{4}{3}b^2

This expression has fractional coefficients. Let's try to factor out a common term. We can factor out 3 from all terms. This will make the first term a2a^2.

3a2+4ab+43b2=3(a2+43ab+49b2)3a^2 + 4ab + \frac{4}{3}b^2 = 3\left(a^2 + \frac{4}{3}ab + \frac{4}{9}b^2\right)

Now, let's look at the expression inside the parenthesis. The first term is a2a^2, which is the square of aa. The last term is 49b2\frac{4}{9}b^2, which is the square of 23b\frac{2}{3}b. The middle term is 43ab\frac{4}{3}ab. Let's check if it is 2×(a)×(23b)2 \times (a) \times \left(\frac{2}{3}b\right). 2×(a)×(23b)=43ab2 \times (a) \times \left(\frac{2}{3}b\right) = \frac{4}{3}ab. This matches the middle term. So, the expression inside is a perfect square.

=3((a)2+2(a)(23b)+(23b)2)= 3\left((a)^2 + 2(a)\left(\frac{2}{3}b\right) + \left(\frac{2}{3}b\right)^2\right)

=3(a+23b)2= 3\left(a + \frac{2}{3}b\right)^2

3(a+23b)2\boxed{3\left(a + \frac{2}{3}b\right)^2}

Step 6 — Factor 95s2+6sv+5v2\frac{9}{5}s^2 + 6sv + 5v^2

This expression also has fractional coefficients. Let's try to factor out a common term. We can factor out 95\frac{9}{5} from all terms. This will make the first term s2s^2.

95s2+6sv+5v2=95(s2+6×59sv+5×59v2)\frac{9}{5}s^2 + 6sv + 5v^2 = \frac{9}{5}\left(s^2 + 6 \times \frac{5}{9}sv + 5 \times \frac{5}{9}v^2\right)

=95(s2+309sv+259v2)= \frac{9}{5}\left(s^2 + \frac{30}{9}sv + \frac{25}{9}v^2\right)

=95(s2+103sv+259v2)= \frac{9}{5}\left(s^2 + \frac{10}{3}sv + \frac{25}{9}v^2\right)

Now, let's look at the expression inside the parenthesis. The first term is s2s^2, which is the square of ss. The last term is 259v2\frac{25}{9}v^2, which is the square of 53v\frac{5}{3}v. The middle term is 103sv\frac{10}{3}sv. Let's check if it is 2×(s)×(53v)2 \times (s) \times \left(\frac{5}{3}v\right). 2×(s)×(53v)=103sv2 \times (s) \times \left(\frac{5}{3}v\right) = \frac{10}{3}sv. This matches the middle term. So, the expression inside is a perfect square.

=95((s)2+2(s)(53v)+(53v)2)= \frac{9}{5}\left((s)^2 + 2(s)\left(\frac{5}{3}v\right) + \left(\frac{5}{3}v\right)^2\right)

=95(s+53v)2= \frac{9}{5}\left(s + \frac{5}{3}v\right)^2

95(s+53v)2\boxed{\frac{9}{5}\left(s + \frac{5}{3}v\right)^2}

Answer

(i) (3x+4y)2(3x + 4y)^2 (ii) (2s+5t)2(2s + 5t)^2 (iii) (7x+2y)2(7x + 2y)^2 (iv) (8p+23q)2\left(8p + \frac{2}{3}q\right)^2 (v) 3(a+23b)23\left(a + \frac{2}{3}b\right)^2 (vi) 95(s+53v)2\frac{9}{5}\left(s + \frac{5}{3}v\right)^2

More questions in Exercise 4.2

Q1

Factor completely:

(i) 9x2+24xy+16y29x^2 + 24xy + 16y^2

(ii) 4s2+20st+25t24s^2 + 20st + 25t^2

(iii) 49x2+28xy+4y249x^2 + 28xy + 4y^2

(iv) 64p2+323pq+49q264p^2 + \frac{32}{3}pq + \frac{4}{9}q^2

*(v) 3a2+4ab+43b23a^2 + 4ab + \frac{4}{3}b^2

*(vi) 95s2+6sv+5v2\frac{9}{5}s^2 + 6sv + 5v^2

(Hint: 2 was taken out as a common factor in Example 7. Is it possible to do something similar in Exercises (v) and (vi) above?)

Q2

Find the values of the following using the identity (ab)2=a22ab+b2(a - b)^2 = a^2 - 2ab + b^2.

(i) (79)2(79)^2

(ii) (193)2(193)^2

(iii) (299)2(299)^2

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