Question

Y is directly proportional to the square of x

When x = 3, y = 25

a) Find an expression for y in terms of x
b) Calculate y when x =4
c) Calculate x when y = 9

Answer 1

a. y=25/9(x^2)

b. y=44.44

c. x=1.8

Explanation:

y=kx^2

a)

y=k*x^2

x=3 y=25

25=k*3^2

25=k*9

25=9k

k=25/9

y=25/9(x^2)

b)

when x=4, y=?

y=25/9(x^2)

y=25/9(4^2)

=25/9(16)

=400/9

=44.44

y=44.44

c)

x=? y=9

y=25/9(x^2)

9=25/9x^2

x^2=9÷25/9

=9×9/25

x^2=81/25

x=√81/25

=9/5

x=1.8