64th B.P.S.C. (Pre) 2018

If $(5)^{x^2+2x+7} = (125)^{2x+1}$ then the value of x is- 6. If $3^{x+8} = 27^{2x+1}$, then the value of x is –

a9
b1✓ Correct
c1
d10
e10

Explanation

$3^{x+8} = 27^{2x+1}$ $3^{x+8} = (3^3)^{2x+1}$ $3^{x+8} = 3^{6x+3}$ Since the bases of both sides are the same, therefore the powers will also be equal. $\therefore x + 8 = 6x + 3$ $6x - x = 8 - 3$ $5x = 5$ $x = 1$

general-mental-ability