Remembering algebra!

je99 · 2007-12-11 11:34:50

Hi!
I know it might be simple but I just don't really remember this from high school and for that reason I found the professors method different.

Find the equation of the line satisfying these conditions:

a. through (3, -6) and vertical

b. through (5, 8); perpendicular to 6x + 8y= 94

mathsyperson · 2007-12-11 14:07:27

1) The line is vertical, so its equation is of the form x=c, where c is some constant. (3,-6) is on the line, and so the line is x=3.

2) First we need to find the gradient of the line that the required line is perpendicular to.
Manipulating it to get y as the subject shows that y = -3/4x + 94/8, and so the gradient is -3/4.

Perpendicular lines have gradients that multiply to -1, and so the required line has a gradient of 4/3.

Now we substitute that along with the given co-ordinates to find the y-intercept.
y = 4/3x + c.
8 = 4/3*5 + c
c = 8 - (4/3)*5 = 4/3

Hence, y = 4/3x + 4/3, or to neaten it up, 3y = 4(x+1).

je99 · 2007-12-12 02:27:43

Thank you!

I was also trying to solve this. But I understand it when I have all the variables.

1. Solve the 3 equation with three variables:

x - y + 5z= -9
5x + z = -1
x+ 4y+ z =15

luca-deltodesco · 2007-12-12 03:24:07

solving it by manipulation

x - y + 5z= -9
5x + z = -1
x+ 4y+ z =15

-24x-y = -4
5x+z = -1
5y-4z = 24

y = 4-24x
z = -1-5x

5(4-24x)+4(1+5x)=24
4*5x-24*5x=0

x = 0
y = 4
z = -1

solving it via matrices:

x = 0
y = 4
z = -1

Last edited by luca-deltodesco (2007-12-12 03:28:52)

je99 · 2007-12-12 05:12:11

Is there any way of solving it via elimination method??

je99 · 2007-12-12 09:47:06

Here is an interesting problem! (I can't use a graphing calculator!

A die is rolled 20 times and the number of twos that come up is tallied. Find the probability of getting the given result:

more than three twos

mathsyperson · 2007-12-12 10:17:11

That's equivalent to the probability of not getting two 2's or less, which in turn is the same as not getting no 2's or one 2 or two 2's.

The probability of each of those can be found with the binomial distribution:

For n trials, each with a probability p of succeeding, the probability that exactly x of them succeed is given by

Math Is Fun Forum

#1 2007-12-11 11:34:50

Remembering algebra!

#2 2007-12-11 14:07:27

Re: Remembering algebra!

#3 2007-12-12 02:27:43

Re: Remembering algebra!

#4 2007-12-12 03:24:07

Re: Remembering algebra!

#5 2007-12-12 05:12:11

Re: Remembering algebra!

#6 2007-12-12 09:47:06

Re: Remembering algebra!

#7 2007-12-12 10:17:11

Re: Remembering algebra!

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