Đáp án:
`e)sqrt{49a^2}+3a(a>=0)=\sqrt{(7a)^2}+3a=|7a|+3a=7a+3a(do\ a>=0)=10a` $\\$ `f)5\sqrt{25a^2}-25a(a<=0)=5\sqrt{(5a)^2}-25a=5|5a|-25a=-25a-25a(do\ a<=0)=-50a` `g)A=4sqrtx-((x+6sqrtx+9)(sqrtx-3))/(x-9)(0<=x,x ne 9)=4sqrtx-((sqrtx+3)^2(sqrtx-3))/((sqrtx-3)(sqrtx+3))=4sqrtx-(sqrtx+3)=3sqrtx-3` $\\$ `B=5sqrtx-((x-10sqrtx+25)(sqrtx+5))/(x-25)=5sqrtx-((sqrtx-5)^2(sqrtx+5))/((sqrtx-5)(sqrtx+5))=5sqrtx-(sqrtx-5)=4sqrtx+5` $\\$ `C=\sqrt{9x^2+12x+4}/(3x+2)(x ne -2/3)=\sqrt{(3x+2)^2}/(3x+2)=|3x+2|/(3x+2)`
