cos(2x) / sin(x) + sin(2x) / cos(x) = csc(x)
Prove that it is an identity.
I've been stuck on this for hours and would really appreciate it if anyone could help.
Prove that it is an identity.
I've been stuck on this for hours and would really appreciate it if anyone could help.
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[(cos 2x)/sin x] + [(sin 2x)/cos x] = csc x
cos 2x = 1 - 2 sin^2 x
sin 2x = 2 sin x cos x
first term...[(1 - 2 sin^2 x)/sin x]
second term...[(2 sin x cos x)/cos x] = 2 sin x
LCD: sin x
so,
[(1 - 2 sin^2 x) + (2 sin^2 x)]/sin x = 1/sin x = csc x
QED
...if you have been stuck for "hours," then go to your teacher for help, immediately...this was not hard ! Study double angle identities...
cos 2x = 1 - 2 sin^2 x
sin 2x = 2 sin x cos x
first term...[(1 - 2 sin^2 x)/sin x]
second term...[(2 sin x cos x)/cos x] = 2 sin x
LCD: sin x
so,
[(1 - 2 sin^2 x) + (2 sin^2 x)]/sin x = 1/sin x = csc x
QED
...if you have been stuck for "hours," then go to your teacher for help, immediately...this was not hard ! Study double angle identities...
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[cos(2x) ⁄ sin(x)] + [sin(2x) ⁄ cos(x)] = 1 ⁄ sin(x)
... common denominator ...
[ cos(x) • cos(2x) + sin(x) • sin(2x) ] ⁄ [sin(x) • cos(x)] = 1 ⁄ sin(x)
... cancel sin(x) ...
[ cos(x) • cos(2x) + sin(x) • sin(2x) ] ⁄ cos(x) = 1
... substitute double angle identities ...
[ cos(x) • { cos²(x) − sin²(x) } + sin(x) • { 2sin(x) • cos(x) } ] ⁄ cos(x) = 1
... cancel cos(x) ...
cos²(x) − sin²(x) + 2sin(x) • sin(x) = 1
cos²(x) − sin²(x) + 2sin²(x) = 1
cos²(x) + sin²(x) = 1
... common denominator ...
[ cos(x) • cos(2x) + sin(x) • sin(2x) ] ⁄ [sin(x) • cos(x)] = 1 ⁄ sin(x)
... cancel sin(x) ...
[ cos(x) • cos(2x) + sin(x) • sin(2x) ] ⁄ cos(x) = 1
... substitute double angle identities ...
[ cos(x) • { cos²(x) − sin²(x) } + sin(x) • { 2sin(x) • cos(x) } ] ⁄ cos(x) = 1
... cancel cos(x) ...
cos²(x) − sin²(x) + 2sin(x) • sin(x) = 1
cos²(x) − sin²(x) + 2sin²(x) = 1
cos²(x) + sin²(x) = 1