Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**ineedhelp****Member**- Registered: 2006-01-21
- Posts: 7

I have two homework problems that I'm not sure I got right. If someone could tell me if my answer is correct that would be great. If its not right, i'll try to solve it again.

Suppose the sales of a particular brand of appliance satisfy the relationship: S(x) = 140x + 100 where S(x) represents the number of sales in year x, with x = 0 corresponding to 1982. Find the number of sales in 1987.

S(x) = 140(5) + 100

I came up with Sales in 1987 were 800.

Decide whether the pair of lines is parallel, perpendicular, or neither: the line through (3, -5) and (-1, 7) and the line through the points (6, -13) and (-2,11)

The first line slope is 2/2 and and the second line slope is -2/4. I came up with neither, because the the slope would be the same if parallel or reciprocal if perpendicular. In this case they are niether.

Offline

**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

The first answer is fine.

In the second one, the gradients need to be calculated differently.

Between (3, -5) and (-1, 7), there is a gradient of

Similarly, between (6, -13) and (-2, 11), there is a gradient of

They have the same gradient and so are parallel.

Why did the vector cross the road?

It wanted to be normal.

Offline

**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,631

And the computer can give you a little help with the straight line graph calculator

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

Offline

**mikau****Member**- Registered: 2005-08-22
- Posts: 1,504

What the heck is gradients? Oddly my mathbook never mentioned that term.

A logarithm is just a misspelled algorithm.

Offline

**ineedhelp****Member**- Registered: 2006-01-21
- Posts: 7

mathsyperson wrote:

The first answer is fine.

In the second one, the gradients need to be calculated differently.

Between (3, -5) and (-1, 7), there is a gradient of

Similarly, between (6, -13) and (-2, 11), there is a gradient of

They have the same gradient and so are parallel.

I see my mistake. I did 7-5 and -1+3 to get 2/2 and 11-13 and -2+6 to get -2/4. I'll fix it. Thanks.

Offline

**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

mikau wrote:

What the heck is gradients? Oddly my mathbook never mentioned that term.

A gradient is just the slope of a line. Well, it's actually the slope of a curve at a given point, but it's most commonly applied to lines. It's basically an less technical way of saying dy/dx.

Why did the vector cross the road?

It wanted to be normal.

Offline

Pages: **1**