Question

y varies directly as x and inversely as the square of z. y=15 when x=80 and z=4. find y when x=81 and z=3

Answer 1

\[y(x,z)\propto xz^{-2}\]\[y(x,z)=kxz^{-2}\]

Answer 2

\[y(80,4)=k(80)(4)^{-2}=15\]

Answer 3

\[k=15\times4^2\div80\]

Answer 4

\[y(81,3)=(15\times4^2\div80)(81)(3)^{-2}=\cdots\]

Answer 5

i came up with 3

Answer 6

did you understand the method /

Answer 7

getting k first

Answer 8

yeah read 'varies directly' as 'proportional to' as 'is a constant multiple of'

Answer 9

three is good

Answer 10

i dont think i am doing the equation right

Answer 11

i also get 27 O_o

Answer 12

\[3^{-2}=\frac 1{3^2}\]

Answer 13

i did 15*16/80

Answer 14

=3

Answer 15

that is right

Answer 16

thanks for the help

Answer 17

anytime