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91Ó°ÊÓ

In Problems 45-52, find the exact value of each expression.

sin5Ï€8.

Short Answer

Expert verified

The exact expression forsin5Ï€8is,1+222.

Step by step solution

01

Step 1 Given expression is,

sin5Ï€8.

Let role="math" localid="1646649909794" sin5π8=sin112.5∘.

role="math" localid="1646649902351" sin112.5∘=sin90∘+22.5∘

We know that,sinA+B=sinAcosB+cosAsinB

02

Step 2 Apply the formula in the expression.

sin90∘+22.5∘=sin90∘cos22.5∘+cos90∘sin22.5∘=1cos22.5∘+0sin22.5∘=cos22.5∘

Now find the value of cos22.5∘by using the Half angle formula.

cosθ2=±1+cosθ2

03

Step 3 Since 22.5∘ lies in the first quadrant, it value should be in positive.

cos22.5∘=cos45∘2=1+cos45∘2=121+12=1+222

Hence,sin5Ï€8=1+222.

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