Simplify them first

Geometry Level 1

sin A , cos A , tan A \sin A , \cos A , \tan A

The product of all the 3 real numbers above is 0.

What is the absolute value of the sum of all these 3 numbers?


The answer is 1.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

4 solutions

Sharky Kesa
Jan 8, 2017

Firstly, note that tan A = sin A cos A \tan A = \dfrac{\sin A}{\cos A} , so cos A 0 \cos A \neq 0 (since tan A \tan A would have an undefined value, so the product would have an indeterminate value). Thus, if we multiply the three real numbers, we get sin 2 A = 0 \sin^2 A = 0 , so A = k π A=k\pi . If sin A = 0 \sin A = 0 , then tan A = 0 \tan A = 0 , and cos A = ± 1 \cos A = \pm 1 , so the absolute value of the sum is 1 \boxed{1} .

Freddie Hand
Jan 8, 2017

Say A = 0 A=0 Then sin A=0 so the product of the three real numbers is 0. So s i n A + c o s A + t a n A = 0 + 1 + 0 = 1 sin A+cos A+tan A=0+1+0=1

You have only shown that the answer is "Yes" if "A=0".

Are you sure that for all A A satisfying the given condition, the answer is still "Yes"?

Pi Han Goh - 4 years, 5 months ago

If A = 360 k A=360k for integral k then the sum is 1, but if A = 180 + 360 k A=180+360k then the sum is -1

Freddie Hand - 4 years, 5 months ago

Log in to reply

Ahhh, that's great. I was wondering why no one reported my problem despite having 7 solvers already.

Let me fix the question now.

Pi Han Goh - 4 years, 5 months ago
Zach Abueg
Jan 8, 2017

t a n tan A = s i n A c o s A A = \frac {sin A}{cos A}

c o s cos A 0 A \neq 0 , so s i n sin A A must be 0. 0. When s i n sin A = 0 , A = 0, t a n tan A = 0 , A = 0, so the product of these three numbers is : :

s i n sin A × c o s A \times cos A × t a n A \times tan A = A =

0 × c o s 0 \times cos A × 0 = 0 A \times 0 = 0

For what values of A A is s i n sin A = 0 A = 0 ? A = 0 , A = π A = 0, A = \pi

Plug them into c o s cos A : A:

c o s cos 0 = 1 0 = 1

c o s cos π = 1 \pi = -1

Because s i n sin A A and t a n tan A A are 0 , 0, the sum of these three numbers is : :

s i n sin A + c o s A + cos A + t a n A + tan A = A =

0 + 1 + 0 = 1 0 + 1 + 0 = 1

o r or

0 1 + 0 = 1 0 - 1 + 0 = -1

Thus, the absolute value of their sum is 1. 1.

Prokash Shakkhar
Jan 8, 2017

Quite Easy! The product of the triplets ( sin A , cos A , tan A ) (\sin A,\cos A,\tan A) =0, if and only one term of the product is 0 0 ... Now Plugging A = 0 A=0 we get, sin 0 cos 0 tan 0 = 0 1 0 = 0 \sin 0*\cos 0*\tan 0 =0*1*0=0 So, \Rightarrow (0+1+0)=\boxed{\color\red{1}}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...