The expression is 4cos40cos50−4sin27.5sin17.5 (in degrees.)
I got 0, with the following strategy
4[1/2(cos10+cos90)]−4[12(cos10−cos45)using product identities and then
2cos10+2cos90−2cos10−2cos90=0
But when I plug it in a calculator it shows up as √2.
Help please?
Thank you very much!
:P