Question

inverse trigonometry question....

Answer 1

ques,. no. 20

Answer 2

@welshfella

Answer 3

pls dont get confuse with the option , its multiple correct option - type question

Answer 4

im thinking B

Answer 5

what do u think it is

Answer 6

the correct options are B, C and D but i want the explanation of the this ques.

Answer 7

i did it just by finding values on my calculator. I cant think of an analytical method just now.

Answer 8

i got C doing it that way.

Answer 9

Oh
sin pi/10 = cos 2pi/5 so that 's why B is a choice

Answer 10

because sin x = cos ( pi/2 - x)

Answer 11

and if you look at the unit circle you see that cos 2pi/5 = - 3pi/5

Answer 12

i got the answers but got in place of sin(pi/10) , i got cos(pi/10), which is wrong
i dont know which step is wrong of mine

Answer 13

cos 2pi/5 = sin pi/10 not cos pi/10

Answer 14

can u pls see my steps and figure out what mistake i made..

cos[ 1/2 arccos{ cos(-14pi/5) } ]
= cos[ 1/2 arccos{ cos( 3pi - pi/5) } ]
= cos { 1/2 arccos (-cos pi/5) }
= cos { 1/2* -pi/5}
= cos { -pi/10}
= cos(pi/10)

Answer 15

Looks like the 3rd step is wrong

Answer 16

I cant remember this stuff very well - its been a long time

but i checked it on the calculator

looks like it should be

cos(1/2 * 4pi/5)

does that make sense?

Answer 17

this would equal cos 2pi/5 = sin pi/10

Answer 18

note:- -cos pi/5 = cos 4pi/5

so i guess you should have made that conversion first
cos { 1/2 arccos (-cos pi/5) }
= cos { 1/2 arccos (cos 4pi/5) }

Answer 19

cos { 1/2 arccos (cos 4pi/5) }
= cos ( 1/2 * 4pi/5)

Answer 20

oh.. i got it now

Answer 21

yea - you should have changed the negative cos to a positive

Answer 22

yeah... well thanks for ur help

Answer 23

this is a part of trig I cant recall very well!

Answer 24

yw - we got there eventually!!