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I'm really having trouble with these two proofs. Can anyone solve these two? It would be greatly appreciated! I'm having trouble getting one side to equal the other.

1.) (sinθ -1)(tanθ + secθ ) = -cosθ

2.) cos B cot B = csc B - sin B

2007-10-13 13:34:33 · 3 answers · asked by neverisenough 1 in Science & Mathematics Mathematics

3 answers

(I don't know how to type thetas, so I'm using x's)

1.) (sinθ -1)(tanθ + secθ )
= sinx tanx + sinx secx - tanx - secx
= (sin^2x / cosx) + (sinx / cosx) - (sinx / cosx) - (1 / cosx)
= (sin^2x - 1) / cosx
= -cos^2x / cosx
= -cosx

2.) cos B cot B
= cos B (cosB / sin B)
= cos^2 B / sin B
= (1 - sin^2 B) / sin B
= (1 / sin B) - (sin^2 B / sin B)
= csc B - sin B

2007-10-13 14:09:19 · answer #1 · answered by mathgoddess83209 3 · 1 0

Question 1
(sin θ - 1)(sin θ/cos θ + 1/cos θ)
(sin θ - 1)(sinθ + 1) / (cos θ)
(sin ² θ - 1) / cos θ
- (1 - sin ² θ) / cos θ
- cos ² θ / cos θ
- cos θ

Question 2
cos B cos B / sin B
cos ² B / sin B
(1 - sin ² B) / sin B
cosec B - sin B

2007-10-17 17:40:34 · answer #2 · answered by Como 7 · 0 0

1. secT = 1/cosT. tanT = sinT/cosT
(sinT - 1) (sinT/cosT + 1/cosT) = -cosT ?
(sinT - 1)( (sinT + 1)/cosT ) = -cosT ?
(sin²T + sinT - sinT - 1)/cos T = -cosT ?
[from relationship sin²T + cos²T = 1, sin²T - 1 = -cos²T ]
-cos²T/cosT = -cosT ?
-cosT = -cosT qed.

2. cotB = cosB/sinB; cscB = 1/sinB
cosBcotB = cscB - sin B ?
cosB(cosB/sinB) = 1/sinB - sinB ?
cos²B/sinB = (1-sin²B)/sinB ?
(1-sin²B)/sinB = (1-sin²B)/sinB qed.

If you don't know sin²B + cos²B = 1, take a few minutes to prove it to yourself.

2007-10-13 21:15:24 · answer #3 · answered by Mr Placid 7 · 0 0

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