The exact value of cos(13π/8) is 1/2 [tex]\sqrt{2-\sqrt{2} }[/tex].
What is trigonometric ratio?
Trigonometriic ratios are the ratios of the sides of a right angled triangle. sin , cos, tan, sec, cosec, cot are some of the trigonometric ratios. Sin is the ratio of perpendicular and hypotenuse, cos is the ratio if base and hypotenuse, tan is the ratio of perpendicular and base, secant is the ratio of hypotenuse and base, cosecant is the ratio of hypotenuse and perpendicular, cot is the ratio of base and perpendicular.
How to find value?
We have to find the value of cos (13π/8).
We have to use formula which is following:
cos[tex]Θ[/tex]=[tex]\sqrt{1/2(1+cos 2Θ}[/tex]
=[tex]\sqrt{1/2(1+cos(2*13 π/8)}[/tex] (π=[tex]π[/tex])
=[tex]\sqrt{1/2(1+cos(3 π+π/4)}[/tex]
=[tex]\sqrt{1/2(1-cos(π/4)}[/tex]
=[tex]\sqrt{1/2(1-1/\sqrt{2} }[/tex]
=[tex]\sqrt{\sqrt{2}-1/2\sqrt{2} }[/tex]
=1/2[tex]\sqrt{2-\sqrt{2} }[/tex]
Hence the value of cos (13π/8) is [tex]1/2\sqrt{2-\sqrt{2} }[/tex].
Learn more about trigonometric ratios at https://brainly.com/question/24349828
#SPJ2
