Solution
Expression : $$Z=\sqrt{20+\sqrt{20+\sqrt{20+\sqrt{20+.....}}}}$$
=> $$Z=\sqrt{20+Z}$$
Squaring both sides, we get :
=> $$Z^2=20+Z$$
=> $$Z^2-Z-20=0$$
=> $$Z^2+4Z-5Z-20=0$$
=> $$Z(Z+4)-5(Z+4)=0$$
=> $$(Z+4)(Z-5)=0$$
=> $$Z=-4,5$$
But $$Z$$ cannot be negative, => $$Z=5$$
=> Ans - (B)
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