Suppose sinA = 12/13 with 90º≤A≤180º. Suppose also that sinB = -7/25 with -90º≤B≤0º. Find cos(A + B).

Question

anonymous · Answer

can some help please:)

anonymous · Answer

someone:) i mean

campbell_st · Answer

ok... you need to find the missing sides in each triangle

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you should realise that x will be a negative value.... as cos is negative in the 2nd quadrant. 

for angle B

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having found cos(A) and cos(B)

you can use the expansion

cos(A +B) = cos(A0cos(B) - sin(A)sin(B)

hope it helps.

anonymous · Answer

thanks you but the answers i can chose are like fractions??? I'm doing evalutating expressions with the sum and difference identies

anonymous · Answer

Since you know sinA and sinB, you can determine cosA and cosB. Then you plug your values into the cos(A+B) expansion.

anonymous · Answer

the answer could be 253/325; 325/253; -36/325; or -204/325

anonymous · Answer

i dont know how to come to the right answer/

anonymous · Answer

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