Find angle y?

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2 Answers
Mar 6, 2018

35.3 degrees

Explanation:

using the cosine rule:
a^2 = b^2 + c^2 -2b*c*CosA
where:
a = 5.9cm
b = 7cm
c = 10cm
A = angle Y

You can rearrange the formula to make A the subject:
A = cos^-1((a^2 - b^2 - c^2)/(-2*b*c))

You can then very easily substitute the values in to get
35.34902418
Although I would round this to 3 significant figures to get
35.3

Mar 6, 2018

Apply cos rule. 35.34

Explanation:

a^2=b^2+c^2-2(b)(c)cosa

Plug in values

5.9^2=7^2+10^2-2(7)(10)cosa
34.81=49+100-140cosa
34.81-149=-140cosa
114.19/140Cos^-1

=35.34