What is the value of cos(pi-pi/4) ?

The value of cos(pi-pi/4) is -(sqrt(2))/2

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cos(pi-pi/4)

cos (π - \frac{π}{4})

- \frac{2}{2}

Decimal Notation

- 0.70710 \dots

Solution steps

cos (π - \frac{π}{4})

Simplify:

π - \frac{π}{4} = \frac{3 π}{4}

π - \frac{π}{4}

Convert element to fraction:

π = \frac{π 4}{4}

= \frac{π 4}{4} - \frac{π}{4}

Since the denominators are equal, combine the fractions:

\frac{a}{c} \pm \frac{b}{c} = \frac{a \pm b}{c}

= \frac{π 4 - π}{4}

Add similar elements:

4 π - π = 3 π

= \frac{3 π}{4}

= cos (\frac{3 π}{4})

Use the following trivial identity:

cos (\frac{3 π}{4}) = - \frac{2}{2}

cos (\frac{3 π}{4})

cos (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

= - \frac{2}{2}

= - \frac{2}{2}

- csc (\frac{π}{3})

cos (- \frac{3}{4})

tan (2 arccos (\frac{12}{13}))

arctan (- \frac{7}{2})

sin (\frac{3 π}{\frac{1}{3}})