I am kinda lost on this guys. The question is: Find the exact value of the expression Cos(300°+45°) I am prty sure u have to use the angle formula, and i plugged it in, but i am lost now. anyone help me?
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Originally Posted by robdarftw I am kinda lost on this guys. The question is: Find the exact value of the expression Cos(300°+45°) I am prty sure u have to use the angle formula, and i plugged it in, but i am lost now. anyone help me? 300 = (270+30) so we have cos((270+30)+45) = cos(270+30)cos(45) - sin(270+30)sin(45) using cos(A+B) and sin(A+B) with A=270 and B=30 gives: : perhaps there is a shorter way?
Originally Posted by robdarftw I am kinda lost on this guys. The question is: Find the exact value of the expression Cos(300°+45°) I am prty sure u have to use the angle formula, and i plugged it in, but i am lost now. anyone help me? OK, clearly this is . We could write this as . So the angle is , just in the 4th quadrant. Remembering that cosine is positive in the fourth quadrant, we get This can be evaluated using a half-angle formula. Remember that . So . So .
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