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Marina CMI [18]
3 years ago
11

5r^2-38r-16 i must factor by grouping but im very lost

Mathematics
1 answer:
scoray [572]3 years ago
7 0
So let's take this step by step. The only two numbers that will give you 5 is 1 and 5. The numbers that can give you 16 is 1, 2, 4, 8, 16. The whole idea behind factoring is playing with these numbers and seeing what gives you -38. 

Let's set up the factors now: 

(5r + __) (r - __) 

What two numbers could you put in the blanks? If you multiply everything together, you'll have to get 5r^2-38r-16. 

If you play around with the numbers, 2 and 8 could be used. So let's plug them in.

(5r + 2)(r - 8) 

If you multiply them out, you'll get 5r^2 - 40r + 2r - 16, or 5r^2 - 38r -16. Hope that helps. 
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Answer:

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Step-by-step explanation:

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A = A₀×(\frac{1}{2} )^{\frac{t}{h} }.........................................................................(1)

Where

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Therefore an expression that represents the number of days until only 10% remains is

\frac{A}{A_0} ×100=100×(\frac{1}{2} )^{\frac{d}{h}  } = 10 %

(\frac{1}{2} )^{\frac{d}{h}  } =\frac{1}{10}

= ㏑(\frac{1}{2} )^{\frac{d}{h}  }  = ㏑(\frac{1}{10})

= \frac{d}{h}×㏑(\frac{1}{2} ) = ㏑(\frac{1}{10})

\frac{d}{h} = \frac{ln(\frac{1}{10}) }{ln(\frac{1}{2} )} = 3.322

Therefore the expression for the number of days 10 % of Technetium-99m will be remaining is

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