Question Video: Using Cofunction Identities to Evaluate Trigonometric Functions Mathematics • First Year of Secondary School

Video Transcript

Using the fact that cos of 𝜃 is equal to the sin of 90 degrees minus 𝜃, what is the equivalent to the cos of 35 degrees?

So here is the equation that we will use. And we wanna find what’s the equivalent to the cos of 35 degrees. So essentially, we’re replacing 𝜃, which is an angle, with 35 degrees. So we need to take 35 degrees and plug it into the other side of the equation.

So we’ve replaced 𝜃 with 35 degrees. And now we simplify. So we need to take 90 degrees minus 35 degrees. And 90 minus 35 is equal to 55. Therefore, the sin of 55 degrees is equivalent to the cos of 35 degrees.