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If y varies directly s the square root of (x + 1) and y =...

If y varies directly s the square root of (x + 1) and y = 6 when x = 3, find x when y = 9

A.

8

B.

7

C.

6

D.

5

Correct answer is A

y α \sqrt{x + 1}\), y = k\sqrt{x + 1}\)

6 = k3+1

6 = k4

6 = 2k

k = 62 = 3

y = (x+1)

9 = 3(x+1)(divide both side by 3)

93 = 3x+13

3 = x+1(square both sides)

9 = x + 1

x = 9 - 1

x = 8