Surds And Indices Q44

44. If 7(x - y) = 343 and 7(x + y) = 16807, what is the value of x?
A. 4	B. 3
C. 2	D. 1

 

Answer : Option A

Explanation :

7^{(x - y)} = 343 = 7³

=> x - y = 3 ---------------------------(Equation 1)

7^{(x + y)} = 16807 = 7⁵

=> x + y = 5 ---------------------------(Equation 2)

(Equation 1)+ (Equation 2) => 2x = 3 + 5 = 8

=> x = ⁸⁄₂ = 4