Question

i posted this question up before but it didn't show up. anyways.. i need help determining whether these two statements are true or not. i tried converting them into square roots but never got the right answer. like cos30=square root 3/2. here they are
1. cos150deg+cos30deg=cos180deg
2. cos(30deg+90deg)=cos30degcos90deg-sin30degsin90deg
thankyou

Answer 1

1. definitely WRONG
cos(A+B) = cosAcosB - sinAsinB
which was used correctly in 2.
but would have been contradicted in 1.

Answer 2

ok thnks.