x is partly constant and partly varies as y .when y=5,x =7;and when y=7 x=8.find the law of variation and also x when y=11

Answer 1

x = ky+m

7 = 5k+m
8 = 7k+m
so, k = 1/2 and m = 9/2
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Answer 2

x=a and x=ky

[x=a+ky]
when x=7 ,y=5
x=a+ky
7=a+5k
a+5k=7 eqn [1]

when x=8,y=7
x=a+ky
8=a+7k
a+7k=8
subtract eqn 1 from eqn 2
a-a+7k-5k=8-7
2k=1
k=1\2
substitute k=1\2 in eqn 1
a+5k=7
a+5[1/2]=7
a+5/2=7
a=7-5/2
a=14-5/2
a=9/2

[x=9/2+1/2]
find x when y=11
x=9/2+1/2[11]
x=9/2+11/2
x=9+11/2
x=20/2
x=10

Answer 3

This is so helpful...