Question

If $9,x,x,49$ are in proportion, find the value of $x$.

Answer 1

$9,x,x,49$ are in proportion,

$\frac{9}{x}=\frac{x}{49}$

$\therefore x^2=9\times 49$

$x=\sqrt{9\times 49}$

$x=\sqrt{9}\times \sqrt{49}$

$x=\pm (3\times 7)$

$x=21$ or $x=-21$