Question

(3x + 7)2 - 84x = (3x – 7)?​

Answer 1

Answer:

LHS = (3x + 7)2 – 84x

RHS = (3x – 7)2

Consider LHS (3x + 7)2 – 84x

Using the identity

(a + b) 2 = a2 + b2 + 2ab

(3x + 7)2 = (3x)2 + 72 + 2 × 3x × 7

(3x + 7)2 = 9x2 + 49 + 42x

∴ (3x + 7)2 – 84x = 9x2 + 49 + 42x – 84x

(3x + 7)2 – 84x = 9x2 + 49 – 42x

∴ LHS = 9x2 + 49 – 42x

Now consider RHS = (3x – 7)2

RHS = (3x – 7)2

Using the identity

(a – b) 2 = a2 + b2 – 2ab

(3x – 7)2 = (3x)2 + 72 – 2 × 3x × 7

(3x – 7)2 = 9x2 + 49 – 42x

∴ RHS = 9x2 + 49 – 42x

Thus LHS = RHS

Hence proved.

Answer 2

Answer:

(3x + 7)2 - 84x = (3x – 7)

6x+14-84x=3x-7

81x=21

x=21/81