WAEC - Mathematics (2008 - No. 19)
If cos (x + 25)o = sin 45o, find the value of x
20
30
45
60
Explanation
cos(x + 25o) = sin 45o
using cos \(\theta\) = sin(90 - \(\theta\))
cos(x + 25o) = cos(90 - 45)
cos(x + 25o) = cos 45
x + 25 = 45
x = 45 - 25
x = 20o
using cos \(\theta\) = sin(90 - \(\theta\))
cos(x + 25o) = cos(90 - 45)
cos(x + 25o) = cos 45
x + 25 = 45
x = 45 - 25
x = 20o
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