SOLUTION: Prove the identity i) cotx - cot2x = cosec2x ii) Show that *integral* (with limit pi/4 and pi/6) cot x dx = 1/2 ln 2. iii) Find the exact value of *integral* (with limit pi/4

Algebra ->  Test -> SOLUTION: Prove the identity i) cotx - cot2x = cosec2x ii) Show that *integral* (with limit pi/4 and pi/6) cot x dx = 1/2 ln 2. iii) Find the exact value of *integral* (with limit pi/4       Log On


   



Question 1206383: Prove the identity
i) cotx - cot2x = cosec2x
ii) Show that *integral* (with limit pi/4 and pi/6) cot x dx = 1/2 ln 2.
iii) Find the exact value of *integral* (with limit pi/4 and pi/6) cosec 2x dx, giving your answer in the form alnb.

Found 3 solutions by Edwin McCravy, mccravyedwin, AnlytcPhil:
Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
i)

cot%5E%22%22%28x%29+-+cot%5E%22%22%282x%29%22%22=%22%22cosec%282x%5E%22%22%29

cos%5E%22%22%28x%29%2Fsin%5E%22%22%28x%29-cos%5E%22%22%282x%29%2Fsin%5E%22%22%282x%29











%28cos%5E2%28x%29%2Bsin%5E2%28x%29%29%2F%282sin%5E%22%22%28x%29cos%5E%22%22%28x%29%29

1%5E%22%22%2F%282sin%5E%22%22%28x%29cos%5E%22%22%28x%29%29

Change the denominator back to sin(2x)

1%5E%22%22%2Fsin%5E%22%22%282x%29

cosec%282x%5E%22%22%29

Edwin


Answer by mccravyedwin(408) About Me  (Show Source):
You can put this solution on YOUR website!
ii) Show that *integral* (with limit pi/4 and pi/6) cot x dx = 1/2 ln 2.

int%28cot%28x%29%2Cdx%2Cpi%2F6%2Cpi%2F4%29%22%22=%22%22ln%28sin%5E%22%22%28x%29%5E%22%22%5E%22%22%29%22%22=%22%22ln%28sin%28pi%2F4%29%5E%22%22%29-ln%28sin%28pi%2F6%29%5E%22%22%29%22%22=%22%22ln%28sqrt%282%29%2F2%29-ln%281%2F2%29%22%22=%22%22%28ln%28sqrt%282%29%29-ln%282%29%5E%22%22%29-%28ln%281%29-ln%282%29%5E%22%22%29%22%22=%22%22

ln%28sqrt%282%29%29-ln%282%29-ln%281%29%2Bln%282%29%22%22=%22%22ln%28sqrt%282%29%29%22%22=%22%22matrix%283%2C1%2C%22%22%2Cln%282%5E%281%2F2%29%29%2C%22%22%29%22%22=%22%22expr%281%2F2%29ln%282%29

Edwin

Answer by AnlytcPhil(1807) About Me  (Show Source):
You can put this solution on YOUR website!
iii) Find the exact value of *integral* (with limit pi/4 and pi/6) cosec 2x dx, giving your answer in the form alnb.

Use the formula:

int%28cosec%28u%5E%22%22%29%2Cdu%29%22%22=%22%22ln%28tan%5E%22%22%28u%2F2%29%5E%22%22%5E%22%22%29%2B+C




int%28cosec%282x%29%2Cdx%2Cpi%2F6%2Cpi%2F4%29%22%22=%22%22expr%281%2F2%29int%28cosec%282x%29%2C%282dx%29%2Cpi%2F6%2Cpi%2F4%29%22%22=%22%22expr%281%2F2%29ln%28tan%5E%22%22%282x%2F2%29%5E%22%22%5E%22%22%29%22%22=%22%22expr%281%2F2%29ln%28tan%5E%22%22%28x%29%5E%22%22%5E%22%22%29%22%22=%22%22%22%22=%22%22expr%281%2F2%29%28ln%281%5E%22%22%29-ln%28sqrt%283%29%2F3%29%5E%22%22%29%22%22=%22%22expr%281%2F2%29%280-ln%28sqrt%283%29%2F3%29%5E%22%22%29%22%22=%22%22

expr%28-1%2F2%29ln%28sqrt%283%29%2F3%29%22%22=%22%22-expr%281%2F2%29%28ln%28sqrt%283%29%29-ln%283%5E%22%22%29%5E%22%22%29%22%22=%22%22%22%22=%22%22expr%28-1%2F2%29%28expr%281%2F2%29ln%283%5E%22%22%29-ln%283%5E%22%22%29%5E%22%22%29%22%22=%22%22expr%28-1%2F2%29%28-expr%281%2F2%29ln%283%5E%22%22%29%5E%22%22%29%22%22=%22%22expr%281%2F4%29ln%283%5E%22%22%29

Edwin