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In Problems 19–28, use the Half-angle Formulas to find the exact value of each expression.

tan7Ï€8

Short Answer

Expert verified

The exact value of the expression tan7Ï€8by using Half angle formula is 1-2

Step by step solution

01

Step 1. Given

An expressiontan7Ï€8

To find the exact value of the expression

02

Step 2. Half angle formula

The half angle formula is,

tanα2=±1-cosα1+cosα

03

Step 3. Consider an angle

Consider,

tanα=tan7π8α=7π8α2=7π42

Let α=7π4

We know that, tanα2=1-cosαsinα

04

Step 4. Use the half-angle formula

By Half-angle formula,

tanα2=1-cosαsinα

Compute for cosα,sinα

cos7π4=cos(2π-π4)=cos(-π4)=cosπ4=22

sin7π4=sin(2π-π4)=sin(-π4)=-sinπ4=-22

05

Step 5. Find the exact value

Since tanα2=1-cosαsinα

tan7Ï€42=1-22-22=2-22-22=-(2-22)=1-2

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