2018年3月7日 · sin −90 = sin(360 − 90) = sin270 Angle 270∘ is third quadrant, where only tan and cot are positive. Hence sin270 = sin(180 +90) = − sin90 = −1

2019年6月27日 · More explanation - sin and cos are complementary to each other, that's where the name came from - sine and cosine . Complementary angles in a triangle are x and 90-x.

2015年12月17日 · Use the sine angle subtraction formula: sin(α −β) = sin(α)cos(β) −cos(α)sin(β) Therefore, sin(x − 90˚) = sin(x)cos(90˚) − cos(x)sin(90˚) = sin(x)(0 ...

2015年5月13日 · Consider that -90° corresponds to 270° (the minus sign is to turn clockwise instead of counter-clockwise): so: sin (-90°)=sin (270°)=-1

2020年12月29日 · As θ → 90∘ θ → 90 ∘, O H → 1 O H → 1. Because O and H become closer and closer to the same value. You can see that on your graph (just keep track of the colors, …

2016年6月30日 · I prefer a geometric proof. See below. If you're looking for a rigorous proof, I'm sorry - I'm not good at those. I'm sure another Socratic contributor like George C. could do …

2020年12月11日 · If you a want to know how is sin(90∘) = 1 sin (90 ∘) = 1 from a triangle's point of view, well you can take any right angled triangle and fix the base length. Now increase the …

2019年4月8日 · Then sin(θ) sin (θ) is the y y coordinate of the point you reached at the end of that path, and cos(θ) cos (θ) is the x x coordinate of that same point. Now let's try to find the sine of …

2015年4月17日 · Note that the image below is only for x in Q1 (the first quadrant). If you wish you should be able to draw it with x in any quadrant. Definition of sin(x) (side opposite angle …

2015年8月14日 · sin(90 +x) = cosx Method 1: Using plots of sinx and cosx. A shift of -90 degrees of sinx gives you cosx Method 2: sin(A± B) = sinAcosB ± cosAsinB