Question

Please help me, I will give medal:)
The value of y varies directly with x^2(x squared),and y=150 when x=5.What is the value of y when x=3?

Answer 1

as this is direct variation we can write
y = k x^2 where k is a constant

Answer 2

ok, so would I square 3?

Answer 3

given that y = 150 when x = 5:-

150 = k * 5^2

can you work out what k is ?

Answer 4

ummmm, no :(

Answer 5

leave the squaring of 3 until later
the first part of the solution is to find the value of k

Answer 6

5^2 = 25 right?

Answer 7

yes

Answer 8

so that would be K?

Answer 9

ok so we have 25k = 150
and to find k we divide both sides by 25

so k = 150 /25 = ?

Answer 10

6

Answer 11

right now we have the values of k
k is called the constant of variation
now we have established the relationship between y and x

it is

y = 6x ( replacing k by 6)

Answer 12

now we can answer the quest ' What is y when x = 3

Answer 13

oops sorry
thats y = 6x^2 not 6x

Answer 14

y=9?

Answer 15

so when x = 3

y = 6 * (3)^2

Answer 16

y=54

Answer 17

right

Answer 18

yay!thank you so much for helping me :D

Answer 19

yw