• # question_answer If 9, $x$,$x$, 49 are in proportion, find the value of $x$ A)  7                                            B)  14C)  21                           D) 35

Given 9,x,x, 49 are in proportion. $\Rightarrow 9\times 49=x\times x$ $\Rightarrow 3\times 3\times 7\times 7=x\times x$ $\Rightarrow (3\times 7)\times (3\times 7)=x\times x$ $\Rightarrow x=3\times 7=21$