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The number of bacteria present in a culture at time t hours is modeled by the continuous variable N and the relationship N = 2000e^kt, where k is a constant. Given that when t = 3, N = 18 000, find (a) the value of k to 3 significant figures

putting in the conditions: 18000 = 2000e^3k ..  ln(9) = 3k .. k=(1/3)ln(9)

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Answered by Benjamin C. Maths tutor
4639 Views

A circle has the equation x^2 + y^2 - 4x + 10y - 115 = 0. Express the equation in the form (x - a)^2 + (y - b)^2 = k, and find the centre and radius of the circle.

Rearrange the equation so that the x terms and y terms bracketed together, like so: (x^2 - 4x) + (y^2 + 10y) - 115 = 0. Complete the square on both sets of brackets, giving (x - 2)^2 - 4 + (y + 5)^2 - 25 ...

Answered by Joseph B. Maths tutor
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Express 160 as a product of its prime factors

Divide 160 by 2 as many times as you can to get 80x2, 40x2x2, 20x2x2x2, 10x2x2x2x2, 5x2x2x2x2x2. Then re-write your answer so that it is 5x2^5. If you're struggling to divide by 2 and keep track of how ma...

Answered by Rachel K. Maths tutor
35490 Views

Use factorisation to solve the equation x^2+5x+6=0

As we are considering a quadratic equation, we are looking for two values of x that make the equation equal to 0. To factorise, first look to the constant term (the term without any x) to find 2 numbers t...

Answered by Niamh C. Maths tutor
2828 Views

Solve 7x-4=8+5x

First bring all the x terms to one side by taking 5x from each side, this gives 2x-4=8. Now put all the number terms on the other side by adding 4 to each side, this gives 2x=12. We can now divide both si...

Answered by Angus M. Maths tutor
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