Exploring Algebraic Identities | Exercise 4.2

Question 2

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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Solution

We will use the given identity (ab)2=a22ab+b2(a - b)^2 = a^2 - 2ab + b^2 to find the squares.

Step 1 — Calculate (79)2(79)^2

Let's express 79 as a difference. We can write 79 as 80 - 1. Here, a = 80 and b = 1.

(79)2=(801)2(79)^2 = (80 - 1)^2

=(80)22×80×1+(1)2= (80)^2 - 2 \times 80 \times 1 + (1)^2

=6400160+1= 6400 - 160 + 1

=6240+1= 6240 + 1

6241\boxed{6241}

Step 2 — Calculate (193)2(193)^2

Let's express 193 as a difference. We can write 193 as 200 - 7. Here, a = 200 and b = 7.

(193)2=(2007)2(193)^2 = (200 - 7)^2

=(200)22×200×7+(7)2= (200)^2 - 2 \times 200 \times 7 + (7)^2

=400002800+49= 40000 - 2800 + 49

=37200+49= 37200 + 49

37249\boxed{37249}

Step 3 — Calculate (299)2(299)^2

Let's express 299 as a difference. We can write 299 as 300 - 1. Here, a = 300 and b = 1.

(299)2=(3001)2(299)^2 = (300 - 1)^2

=(300)22×300×1+(1)2= (300)^2 - 2 \times 300 \times 1 + (1)^2

=90000600+1= 90000 - 600 + 1

=89400+1= 89400 + 1

89401\boxed{89401}

Answer

(i) (79)2=6241(79)^2 = 6241 (ii) (193)2=37249(193)^2 = 37249 (iii) (299)2=89401(299)^2 = 89401

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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