# SOLUTION: Use the cofunction identities to evaluate the expression. sin^2 (18 Degrees) + sin^2 (40 Degrees) + Sin^2 (50 Degrees)+ sin^2 (72 Degrees) I'm honestly stumped after hours of

Algebra ->  Algebra  -> Trigonometry-basics -> SOLUTION: Use the cofunction identities to evaluate the expression. sin^2 (18 Degrees) + sin^2 (40 Degrees) + Sin^2 (50 Degrees)+ sin^2 (72 Degrees) I'm honestly stumped after hours of      Log On

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 Click here to see ALL problems on Trigonometry-basics Question 710533: Use the cofunction identities to evaluate the expression. sin^2 (18 Degrees) + sin^2 (40 Degrees) + Sin^2 (50 Degrees)+ sin^2 (72 Degrees) I'm honestly stumped after hours of attempts, will anyone assist me in my struggle?Answer by KMST(1874)   (Show Source): You can put this solution on YOUR website!In a right triangle, the two acute angles are complementary, meaning that their measures add up to . The way sine and cosine were defined based on a right triangle, sine of an angle is the cosine of the complement. (It works if you define sine and cosine based on the unit circle too). Something similar happens with tangent and cotangent, and with secant and cosecant. For all the trigonometric functions the function of an angle equals the cofunction of the complement. Those are the cofunction identities. Since , angles measuring and are complementary, and . Then Also , since , angles measuring and are complementary, and . Then Putting it all together: =