If F(x) = 8x + 10; Find F-1(42).
Solution
HINT: F-1(x) means
inverse.
PROCEDURE:
Make x the subject and then
interchange x and y variables.
Let y=F(x)
So,
y= 8x + 10
y – 10 = 8x
y – 10 = 8x
8 8
y – 10 = x
8
x
= y – 10 after rearranging
8
y-1 = x – 10 after interchanging x and y variables.
8
F-1(x) = x – 10 after interchanging x and y variables.
8
Now we calculate F-1(42)
as hereunder;
F-1(90) = 42 – 10
8
F-1(90) = 32
8
F-1(90) = 4 [after
dividing 32 by 8]
Hence, F-1(32)
= 4
.
TRY THIS……………………………
If F(x) = 7x + 20; Find F-1(14).
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