Answer:

Step-by-step explanation:
To find the area of a triangle, we can use the formula of:

This formula comes from the area of a rectangle, because a triangle is half a rectangle.
We could use the numbers and the difference of the original cost - the end price in a equation.
53 × x/100 = 15.9
Cross multiply 100 × 15.9.
53x=1590
Divide both sides by 53.
x=30
The coupon was 30%
Repeated fractions are written with 9's in the denominator.
0.136 = 136/1000
0.136 repeated = 136/999
Answer:
V=25088π vu
Step-by-step explanation:
Because the curves are a function of "y" it is decided to take the axis of rotation as y
, according to the graph 1 the cutoff points of f(y)₁ and f(y)₂ are ±2
f(y)₁ = 7y²-28; f(y)₂=28-7y²
y=0; x=28-0 ⇒ x=28
x=0; 0 = 7y²-28 ⇒ 7y²=28 ⇒ y²= 28/7 =4 ⇒ y=√4 =±2
Knowing that the volume of a solid of revolution V=πR²h, where R²=(r₁-r₂) and h=dy then:
dV=π(7y²-28-(28-7y²))²dy ⇒dV=π(7y²-28-28+7y²)²dy = 4π(7y²-28)²dy
dV=4π(49y⁴-392y²+784)dy integrating on both sides
∫dV=4π∫(49y⁴-392y²+784)dy ⇒ solving ∫(49y⁴-392y²+784)dy
49∫y⁴dy-392∫y²dy+784∫dy =
V=4π(
) evaluated -2≤y≤2, or 2(0≤y≤2), also
⇒ V=25088π vu