Solve without Calculator

Can I please get help, with this problem? It is actually quite easy when done with a calculator, but I'm actually asked to do it without calculator. Can someone help me solve it without calculator?

#Geometry

Easy Math Editor

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`\sum_{i=1}^3`	$\sum_{i=1}^3$
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Comments

Well, even if we use cosine rule, we still need a calculator to solve for cos(70)........Or, by manipulating it to cos(60+10) and using Taylor expansion for 10 degree.......we may get close to the answer, but it would be tedious......

Aaghaz Mahajan - 3 years, 2 months ago

I thought so. Thank you very much. How would you go about solving it with 60° angle?

César Castro - 3 years, 2 months ago

You are Welcome!!
Well, if the angle was 60 degree, then it's simple since cos(60) = 1/2......

Aaghaz Mahajan - 3 years, 2 months ago

@Aaghaz Mahajan – Hard question

Michael Asare - 3 years, 2 months ago

@Michael Asare – Ummm.....What do u mean??

Aaghaz Mahajan - 3 years, 2 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$