Question

can you check my work please i having trouble with a minus sign here, trying to proof the derivative of sec at point a,

Answer 1

@Preetha @Zarkon :D

Answer 2

@jim_thompson5910 can you spare a minute friend :D

Answer 3

I don't know how you got line 3

Answer 4

hmm let me see

Answer 5

hmm you mean the identity of cos a - cos b

Answer 6

i used that identity

Answer 7

oh ok, I see now

Answer 8

@iambatman can you spare a minute friend

Answer 9

so where are you stuck exactly?

Answer 10

well the answer should be tan(a)*sec(a)

Answer 11

no minus sign

Answer 12

im dont know how to get rid of that minus sign

Answer 13

ok let me look it over once more

Answer 14

hehe ok

Answer 15

ok the issue is how you applied the trig identity

Answer 16

this is what you should have

cos(x) - cos(y) = -2*sin[ (x+y)/2 ]*sin[ (x-y)/2 ]

cos(a) - cos(x) = -2*sin[ (a+x)/2 ]*sin[ (a-x)/2 ]

cos(a) - cos(a+h) = -2*sin[ (a+a+h)/2 ]*sin[ (a-(a+h))/2 ]

cos(a) - cos(a+h) = -2*sin[ (a+a+h)/2 ]*sin[ (a-a-h)/2 ]

cos(a) - cos(a+h) = -2*sin[ (2a+h)/2 ]*sin[ -h/2 ]

cos(a) - cos(a+h) = -2*sin[ (2a+h)/2 ]*(-sin[ h/2 ])

cos(a) - cos(a+h) = 2*sin[ (2a+h)/2 ]*sin[ h/2 ]

Answer 17

ohhh thank, thank my friend :DDD!!!! ,