Sunday, May 24, 2015

What is the inverse of the sentence, "If Sam leaves, then I will stay."?

The logical inverse of an if-then statement p -> q is

~p -> ~q

For us 

p is "if Sam leaves" so ~p is "If Sam does not leave"

and q is "I will stay" so ~q is "I will not stay"

Therefore the inverse is:

If Sam does not leave, then I will not stay.

The element lawrencium has a half-life of 10 hours. What fraction of 1 ounce of lawrencium will remain after 4 days 4 hours?

4 days and 4 hours is 4(24)+4 = 100 hours 
so our quantity is halved 10 times over the time period: 

Q=Q%5B0%5D%2A%281%2F2%29%5E10 

Q=%281%2F1024%29%2AQ%5B0%5D


so its 1/1024 oz

Determine Algebraically whether f(x) = 1 + x + x^2 is even, odd, or neither

A function is even if f(x) = f(-x), but for our function

f(-x)=1-x+x^2

so it is not even.

To be odd -f(x)=f(-x), and for our function

-f(x) = -1-x-x^2

and so it is also not odd.

Therefore it is neither.

Find the twentieth term of the arithmetic sequence with a1 = 15 and d = 4.

For an arithmetic progression we use the formula:

a%5Bn%5D=a%5B1%5D%2B%28n-1%29%2Ad

n=20, a1=15, d=4


a%5B20%5D=15%2B%2820-1%29%2A4

a%5B20%5D=15%2B19%2A4

a%5B20%5D=91

:)

how can i decompose this partial fraction(4x^3)/(x^3-x^2)

This is not a "proper" decomposition problem. Typically the degree of the denominator is greater than the degree of the numerator...
but...we can still simplify...
notice that this expression can be factored:
%284x%5E3%29%2F%28x%5E3-x%5E2%29=%28%28x%5E2%29%284x%29%29%2F%28%28x%5E2%29%28x-1%29%29
from here we notice that by polynomial long division (don't know how to show using this editor) that:
x%2F%28x-1%29=1%2B1%2F%28x-1%29
so our expression simplifies to...

%284%2B4%2F%28x-1%29%29

:)

find a if a(a-8)=20

a(a-8)=20
a%5E2-8a-20=0
%28a-10%29%28a%2B2%29=0

so a= 10 or a=-2