SOLUTION: Evaluate Sec 660degrees + Cot 405degrees without using a calculator. Please show steps thanks you!

Algebra ->  Complex Numbers Imaginary Numbers Solvers and Lesson  -> Lesson -> SOLUTION: Evaluate Sec 660degrees + Cot 405degrees without using a calculator. Please show steps thanks you!      Log On


   



Question 1154166: Evaluate Sec 660degrees + Cot 405degrees without using a calculator. Please show steps thanks you!
Found 3 solutions by josgarithmetic, Alan3354, MathLover1:
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
Do you realize that 405 degrees is 9 times 45 degrees?
Do you realize that 660 degrees is 11 times 60 degrees?

Make reference to the common angles on the unit circle, and take the values for sec(660) and cot(405) that way, and do your computations.

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Evaluate Sec 660degrees + Cot 405degrees
------
Subtract 360
= sec(300) + cot(45)
= 1/cos(300) + 1
= 1/cos(60) + 1
= 2 + 1
= 3

Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

sec%28+660%29+%2B+cot+%28405%29..........express sec%28+660%29 with sin and cos

=1%2Fcos%28+660%29+%2B+cot%28405%29..use identity: cos%28x%29=sin%2890-x%29..since your x=660


=1%2Fsin%2890-660%29+%2B+cot%28405%29

1%2Fsin%28-570%29+%2B+cot%28405%29...........use the following property : sin+%28-x+t%29=-+sin+%28x+%29

=-1%2Fsin%28570%29+%2B+cot%28405%29

rewrite sin%28570%29 .......... apply the periodicity of sin : sin%28570%29=sin%28x%2B360%2Ak%29=sin%28x%29

so, sin%28570%29+=sin%28210%29+


=-1%2Fsin%28210%29+%2B+cot%28405%29................rewrite the angles for cot%28405=360%2B45%29=cot%2845%29


=-1%2Fsin%28210%29+%2B+cot%2845%29......write sin+%28210+%29 as sin+%28180+%2B30+%29


using the summation identity : sin+%28x%2By+%29=+sin++%28x+%29+cos+%28y+%29%2B+cos+%28x+%29+sin+%28y+%29

so you have sin+%28180+%2B30+%29=+sin++%28180+%29+cos+%2830+%29%2B+cos+%28180+%29+sin+%2830+%29

now use the following trivial identities:
sin++%28180+%29=0
cos+%28180+%29=-1
sin+%2830+%29=1%2F2
cos+%2830+%29=sqrt%283%29%2F2
then you have sin+%28180+%2B30+%29=+0%2A++%28sqrt%283%29%2F2+%29%2B+%28-1+%29+%281%2F2+%29=-1%2F2
and cot%2845%29=cos%2845%29%2Fsin%2845%29=%281%2Fsqrt%282%29%29+%2F%281%2Fsqrt%282%29%29=1+

so, you have:

=-1%2F%28-1%2F2%29+%2B+1
=2+%2B+1
=3
=> sec%28+660%29+%2B+cot+%28405%29=3