Which expression is a factor of 21x2 + 13x – 20?A. 3x – 4B. 7x - 5C. 7x + 4D. 3x + 5

Mathematics

1 answer:

LUCKY_DIMON [66]1 year ago

8 0

Answer:

B. 7x - 5

Explanation

Given the expression 21x^2 + 13x – 20, to get which of the given expression is a factor we will have to factorize the equation first as shown;

21x^2 + 13x – 20

= 21x^2 + 28x - 15x - 20

= 7x(3x+4) -5(3x+4)

= (7x-5)(3x+4)

Hence one of the factors is 7x - 5

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Using an exponential equation, supposing a rate of 5%, it is found that it will take about 2.9 years for Emma's balance to reach $450.

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$A(t) = A(0)(1+r)^t$

In which:

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r is the growth rate, as a decimal.

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The growth rate is of 15%, hence R =0.15

Then,

$A(t) = A(0)(1+r)^t$

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$A(t) =300(1.15)^t\\450= 300(1.15)^t\\1.15^t=\frac{450}{300}\\\\1.15^t =1.5\\log(1.15)^t=log1.5\\t log 1.15 = log 1.5\\t = \frac{log1.5}{log1.15}\\\\ t =2.9$