If x `prop y and x prop z,` then (y+z) `prop`

Explanation

`x prop y rArr k_(1) y ( k_(1)` = non -zero variation constant )…..(1)
x `prop z rArr x = k_(2)z (k_(2)`= non -zero variation constant ) ……..(2)
From (1) we get , y `(x) /(k_(1))`…….(3)
From (2) we get ,z = `(x)/(k_(2)) `………(4)
Now , adding (3) and (4) we get , `y+z =(x)/(k_(1))+(x)/(k_(2)) `
` or ,y+z =((x)/(k_(1))+(x)/(k_(2)))x `
` or ,y+z =k.x[when(x)/(k_(1))+(x)/(k_(2))=k] `
`therefore y +zpropx [becausekne0="variation constant"]`
`thereforey +z propx. `