Question

solve by using identities: 12.1 square - 7.9 square by full procedure.

Answer 1

(12.1)^2(7.9)^2
Use the identity a^2-b^2
(a+B)(a-b)
(12.1+7.9)(12.1-7.9)
20*4.2
84

Answer 2

The value of $12.1^{2} -7.9^{2}$= 84.

Step-by-step explanation:

We have,

$12.1^{2} -7.9^{2}$

By using identities, to find the vaue of  $12.1^{2} -7.9^{2}=?$

We know that,

$(a+b)^{2} -(a-b)^{2}=(a^{2}+b^{2}+2ab )-(a^{2}+b^{2}-2ab)$

$=a^{2}+b^{2}+2ab -a^{2}-b^{2}+2ab$

$=4ab$

∴ $(10+2.1)^{2} -(10-2.1)^{2}$

Here, a = 10 and b =2.1

$=4ab$

$=4\times 10 \times 2.1$

$=40 \times 2.1$

= 84

Hence, the value of $12.1^{2} -7.9^{2}$ = 84.