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Core 2 help

ok so the cosine of an obtuse angle BCA is -1/3
and side AB = 9
BC= 6
CA = 5
what is the sine of the angle? I've looked in the markscheme and it comes out as 2/3*root 2
I dunno how you do this.
Reply 1
Avatar for TheStrokess
TheStrokess
OP
yeah this is where i get confused
im completely self teaching core 2 and left it to last minute
erm when you say cos^2 + sin^2 am i squaring the cosine of the angle?
many thanks
Reply 2
Avatar for Woody.
Woody.
12
Cos(x) = -1/3
SOHCAHTOA
Cos(x) = Adjacent/Hypotenuse

(-1)^2 + x^2 = 3^2
x^2 = 8
x = root8

Sin(x) = opposite/hypotenuse
= root8/3 = (2 * root2)/3

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