X is a positive acute angle. That means x is located in the first quadrant and has positive value in sin, cos, tan.
The formula of trigonometry ratio
cos x =

sin x =

From the formula of cosine
cos x =


from the formula above, adjacent side is 3 units, and hypotenuse is 5 units
Draw a right triangle to illustrate the location of the sides. See image attached.
To find the ratio of sine, we need to find the length of opposite side using pythagorean theorem
3² + (opposite)² = 5²
9 + (opposite)² = 25
(opposite)² = 25 - 9
(opposite)² = 16
opposite = 4
The length of opposite side is 4 units
Find sin x
sin x =

sin x =
If you are saying that the hypotenuse is 10 cm the you have to solve the following equation using the Pythagorean theory.
4^2 + b^2 = 10^2
16 + b^2 = 100
16 - 16 + b^2 = 100 - 16
b^2 = 84
Find 
It was about 17.4%
======================================================================
% error=
actual value-estimated value
Then divide that by actual value
16.5 mg of calcium per tablet × 20 tablets=
330 mg of calcium