Công thức lượng giác

sin²a+cos²a

= 1

1 + tan²(a)

1/cos²(a)

1 + cot²(a)

1/sin²(a)

tan(a).cot(a)

= 1

cos(-a)

cos(a)

sin(-a)

- sin(a)

tan(-a)

- tan(a)

cot(-a)

-cot(a)

sin(π-a)

sin(a)

cos(π-a)

-cos(a)

tan(π-a)

-tan(a)

cot(π-a)

-cot(a)

sin(π+a)

-sin(a)

cos(π+a)

-cos(a)

tan(π+a)

tan(a)

cot(π+a)

cot(a)

sin(π/2 - a)

cos(a)

cos(π/2 - a)

sin(a)

tan(π/2 - a)

cot(a)

cot(π/2 - a)

tan(a)

sin(a+ π/2)

cos(a)

cos(a + π/2)

-sin(a)

tan(a +π/2)

-cot(a)

cot(a + π/2)

-tan(a)

sin(a+b)

sin(a)cos(b)+cos(a)sin(b)

sin(a-b)

sin(a)cos(b)-cos(a)sin(b)

cos(a+b)

cos(a)cos(b)-sin(a)sin(b)

cos(a-b)

cos(a)cos(b)+sin(a)sin(b)

tan(a+b)

(tan(a)+tan(b))/(1-tan(a)tan(b))

tan(a-b)

tan(a)-tan(b)/1+tan(a)tan(b)

sin(2a)

2sin(a)cos(a)

cos(2a)

cos²(a) - sin²(a) = 2cos² - 1 = 1 - 2sin²(a)

tan(2a)

2tan(a) / 1-tan²(a)

sin(3a)

3sin(a)-4sin^3(a)

cos(3a)

4cos³(a)-3cos(a)

tan(3a)

(3tan(a)-tan³(a)) /(1-3tan²(a))

cos²(a)

(1+cos(2a))/2

sin²

(1-cos(2a))/2

tan²(a)

(1-cos(2a)) / (1+cos(2a))

cos³(a)

(3cos(a)+ cos(3a)) / 4

sin³a

(3sin(a)-sin(3a)) / 4

sin(a) + sin(b)

2sin((a+b)/2)cos((a-b)/2)

sin(a) - sin(b)

2cos((a+b)/2)sin((a-b)/2)

cos(a) + cos(b)

2cos((A + B)/2)cos((A - B)/2)

cos(a) - cos(b)

-2sin((a-b)/2)sin((a+b)/2)

cos(a)cos(b)

1/2[cos(A-B)+cos(A+B)]

sin(a)sin(b)

1/2[cos(A-B)-cos(A+B)]

sin(a)cos(b)

1/2[sin(A-B)+sin(A+B)]

sin(a)+cos(a)

√2sin(a+π/4) = √2cos(a-π/4)

sin(a)-cos(a)

√2sin(a-π/4) = √2cos(a+π/4)