Question

Find 4ab when (a+b)=15 and (a-b)=12

Answer 1

a + b = 15 ..... eq 1
a – b = 12 ...... eq 2

So a = 15 – b
Substitute in eq 2 :

15 – b – b = 12
15 – 2b = 12
–2b = 12 – 15
b = 1.5

So a = 15 – 3/2 = 13.5

4ab = 4 x 13.5 x 1.5 = 81

Answer 2

81

Explanation:

here,

(a+b)=15 -------(1)

(a-b)=12 -------(2)

Equating the equation (1) and (2)

a + b = 15

a - b = 12

(b gets cancelled having opposite signs)

or, 2a = 27

or, a = 27÷2

a = 13.5

then, putting value of a in equation (1)

a+b=15

or, 13.5 + b=15

or, b=15-13.5

b=1.5

lastly,

4ab = 4×13.5×1.5

= 81

hope it helps!!