Answer:
Step-by-step explanation:
The total amount Rita spent is ...
(18.54x +23) +(25) = 18.54x +48 . . . total spent
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When x=2, that is approximately ...
(18.5)(2) + 48 = 37 +48 = (40 -3) +(50 -2) = (40 +50) -(3 +2) = 90 -5 = 85
Rita spent about $85 if she bought 2 items.
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<em>Additional comment</em>
Estimation is often done using 1 significant figure. In this case, that would mean rounding the equation to 20x+50, so it would give a value of 90 when x=2.
An additional task when estimating is to estimate the error in the estimate. Here, using 20x+50 has an error of approximately 1.5x+2 (too high), so the error for 2 items will be about (1.5(2)+2) = 5. That is, the estimate of 90 is approximately 5 too high. Even this estimate has a remaining small error of 0.04x (too low).
The correct answer is the first option, which is:
(–7 + i) + 7i = –7 + (i + 7i)
The explanation is shown below:
1. By definition, in the associate property of addition you summ the number by grouping them with parenthesis, without matter where you use those parenthesis.
2. Therefore, as you can see, you can obtain the result of the addition by agruping the numbers <span>(–7 + i) + 7i or –7 + (i + 7i)</span> .
Answer:
-30√(t/a) cos(√(at)) + 30/a sin(√(at)) + C
Step-by-step explanation:
∫ 15 sin(√(at)) dt
Use substitution:
If x = √(at), then:
dx = ½ (at)^-½ (a dt)
dx = a / (2√(at)) dt
dx = a/(2x) dt
dt = (2/a) x dx
Plugging in:
∫ 15 sin x (2/a) x dx
30/a ∫ x sin x dx
Integrate by parts:
If u = x, then du = dx.
If dv = sin x dx, then v = -cos x.
∫ u dv = uv − ∫ v du
= 30/a (-x cos x − ∫ -cos x dx)
= 30/a (-x cos x + ∫ cos x dx)
= 30/a (-x cos x + sin x + C)
Substitute back:
30/a (-√(at) cos(√(at)) + sin(√(at)) + C)
-30√(t/a) cos(√(at)) + 30/a sin(√(at)) + C
