The formula you need to know is that the side opposite of the 30° angle is always half the hypotheneus. For example in question 2 X should be 6 since 3 is opposite side of the angle 30°. In a 45 45 90 triangle, it is important to know that the straight sides are always the same length (since they are the same angle). For example in question 9, v is also 9√2.
When you have two sides, you can figure out the third side with a² + b² = c² since they are all right triangles. Good luck
The double implication "if and only if" is graphically represented by an arrow pointing in both direction, so the correct writing is
We know that the profit from an item is the sale price minus the cost price. Thus,
1269 - 0.2x² - 830 - 398x
P(x) = -0.2x² - 398x + 439
Local maxima are located at the points where the first derivative of a function are 0
P'(x) = -0.4x - 398
398 = -0.4x
x = -995
There is only one maximum so the average value is -995
