How do you use cross products to solve 3/x=4/28?

2 Answers
Jim G.
Jan 26, 2017

x=21

Explanation:

color(blue)(3)/color(red)(x)=color(red)(4)/color(blue)(28)

Now multiply the color(red)"values in red" together, the color(blue)"values in blue" together and equate them.

As you can see, this multiplication forms a cross (X) hence the reason it is called cross products.

rArrcolor(red)(4x)=(color(blue)(3)xxcolor(blue)(28))

rArr4x=84

To solve for x, divide both sides by 4

(cancel(4) x)/cancel(4)=84/4

rArrx=21

color(blue)"As a check"

substitute this value into the equation and if the left side equals the right side for this value then it is the solution.

"left side "=3/21=cancel(3)^1/cancel(21)^7=1/7

"right side "=4/28=cancel(4)^1/cancel(28)^7=1/7

rArrx=21" is the solution"

Alan N.
Jan 26, 2017

x=21

Explanation:

3/x = 4/28

3/x = 1/7

Cross multiply:

x xx1 = 3xx7

x=21

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