Explanation:
f (x) = 1 - 5x
g (x) = 2x + 3
find (fog) (x)
it's a composite function so basically we substitute x = 2x + 3 where we see x in f (x) = 1 - 5x
so doing that we'll get
1 - 5(2x + 3)
next expand your brackets
1 - 10x + 15
equate to 0 to make things easier
1 - 10x + 15 = 0
make x the subject
1 + 15 = 10x (this is the same as 10x = 1 + 15)
x = 16/10 (you can leave it as a fraction)
fog(x) = 16/10
find gof (x)
we'll do the same thing again
2(1-5x) + 3
2 -10x + 3 = 0
2 + 3 = 10x
10x = 5
x = 5/10 (reduce)
x = 1/2
gof (x) = 1/2