BÀI 2 : tan a =7/24
Ta cÓ : tan a . cot a = 1
=> cot a = 1/tan a = 1/(7/24)= 24/7
Ta cÓ : 1/cos^2 a =1 + tan^2 a
=> 1/cos^2 a = 1+ (7/24)^2 =625/576
=> cos^2 a = 1/(625/576)=576/625
=> cos a =24/25
LẠI có : tan a = sin a / cos a
=> sin a = tan a .cos a = 7/24 . 24/25 =7/25

BÀI 3
( sin a + cos a )^2 -( sin a -cos a )^2
= sin ^2 a + 2 .sin a .cos a + cos ^2 a -( sin^2 a - 2.sin a.cos a + cos^2 a )
=sin ^2 a + 2 .sin a .cos a + cos ^2 a - sin^2 a +2.sin a.cos a - cos^2 a
=4 .sin a .cos a

bai 5

Có sin^2a + cos^2a = 1 <=> 25/169 + cos^2a = 1
=> cos^2 a= 1 - 25/169 = 144/169 <=> cosa = 7/13
tan a= sina / cos a = 5/7
<=> cot a= 7/5
2) tan a x cot a = 1 => cot a = 1/tan a = 24/7
cos a = cot a/sin a = 576/49
sin a = 49/576

Bai 4
_Cho mk 5 sao va like cho mk nhe_