Answer: A; 6.3%
Step-by-step explanation:
Problem 1
For the first problem, we first want to find y so that we can plug it into the expression.
We can use elimination method for the system of equations to solve.
3x+3y=21
3x-y=5
We subtract both equations to eliminate x.
4y=16 [divide both sides by 4]
y=4
Now that we know y, we can plug it into the expression.
[divide]
[subtract]

We know that the answer is A.
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Problem 2
For the second problem, we need to know how to calculate percent error. The formula for precent error is
. We know that the exact value is 80 because the buyer was supposed to given 80. 75 is the measured value because that was what the buyer was given.
[subtract]
[solve absolue value]
[divide]
[multiply]

Since the problem said to round to one decimal place, we know that the answer is 6.3%.
14.4, 120% of 12 is 100+20, 12+2.4 is 14.4
Answer:
D
Step-by-step explanation:
To convert from polar to rectangular form
• x = rcosΘ , y = rsinΘ
• r =
⇒ r² = x² + y²
Given
r = 8cosΘ
r = 8 ×
( multiply both sides by r )
r² = 8x, hence
x² + y² = 8x ⇒ D