sin a = 12/13 is in second quadrant
cos b = - 4/5 is in third quadrant
equation is sin (a + b)
THANKS IN ADVANCE
sin (a + b); sin a = 12/13; cos b = -4/5. Please help solve?
2015-08-30 10:13 am
回答 (3)
2015-08-30 10:19 am
cos a = -√(1 - (sin a)^2) = -√(1 - 144/169) = -5/13
sin b = -√(1 - (cos b)^2) = -√(1 - 16/25) = -3/5
sin (a + b) = sin a cos b + sin b cos a = -(12/13)(4/5) + (3/5)(5/13)
= -33/65
sin b = -√(1 - (cos b)^2) = -√(1 - 16/25) = -3/5
sin (a + b) = sin a cos b + sin b cos a = -(12/13)(4/5) + (3/5)(5/13)
= -33/65
2015-08-30 3:57 pm
sin a cos b + cos a sin b
[12/13 ] [ -4/5 ] + [- 5/13 ] [- 3/5 ]
-48/65 + 15/65 = - 33/65
[12/13 ] [ -4/5 ] + [- 5/13 ] [- 3/5 ]
-48/65 + 15/65 = - 33/65
2015-08-30 10:21 am
a is in the 2nd quadrant.
sin a = 12/13
cos a = -[√(13² - 12²)]/13 = -5/13
b is in the 3rd quadrant.
cos b = -4/5
sin b = -[√(5² - 4²)]/5 = -3/5
sin (a + b)
= sin a cos b + sin b cos a
= (12/13) × (-4/5) + (-3/5) × (-5/13)
= (-48/65) + (15/65)
= -33/65
sin a = 12/13
cos a = -[√(13² - 12²)]/13 = -5/13
b is in the 3rd quadrant.
cos b = -4/5
sin b = -[√(5² - 4²)]/5 = -3/5
sin (a + b)
= sin a cos b + sin b cos a
= (12/13) × (-4/5) + (-3/5) × (-5/13)
= (-48/65) + (15/65)
= -33/65
收錄日期: 2021-04-18 00:06:45
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