Cross Products

In an equation of the form

we can multiply both sides by bd to get the equation

ad = bc.

This is known by many names: cross-multiplying, taking cross-products, the means-extremes property, or the reciprocal property.

Use the means-extremes property to get a simpler equation.

3(9) = 7(x + 1)

Now simplify and solve.

27 = 7x + 7

7x = 20