Find angle y?

Question

2450 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2018-03-06T18:22:36

35.3 degrees

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

Answer 2 · 2018-03-06T18:33:35

Apply cos rule. 35.34

#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