What is the positive square root of $$[19+4\sqrt21]?$$
Expression : $$[19+4\sqrt21]?$$
= $$[19+2\sqrt{4\times21}]=[19+2\sqrt{84}]$$
= $$7+12+2\sqrt{7\times12}$$
= $$(7)^2+(12)^2+2\sqrt{7\times12}$$
Now, we know that $$a^2+b^2+2ab=(a+b)^2$$
= $$(\sqrt{7}+\sqrt{12})^2$$
Thus, square root is = $$\sqrt{7}+\sqrt{12}$$
=Â $$\sqrt7+2\sqrt3$$
=> Ans - (A)
Create a FREE account and get:
