1)(2+5i)+(1-7i)=(2+1)+(5i-7i)=3-2i
2)(3-9i)-(7+i)=(3+7)-(i-9i)=10+8i
3)(1-5i)*(5+2i)=(1*5+(-5)*2)+i(1*5-(-5)*2)=(5-10)+i(5+10)=-5+i15
