Question

tìm a,b thuộc z

a)15+14+13+...+a=0

b)a.b=a-b

c)10=10+9+8+...+a

d)a(b+2)+b=1

e)a+(a+1)+(a+2)+...+35=0

Answer 1

b: =>ab-a+b-1=-1

=>(a-1)(b-1)=-1

=>\(\left(a-1;b-1\right)\in\left\{\left(1;-1\right);\left(-1;1\right)\right\}\)

=>\(\left(a,b\right)\in\left\{\left(2;0\right);\left(0;2\right)\right\}\)

d: =>a(b+2)+b-1=0

=>a(b+2)+b+2-3=0

=>(a+1)(b+2)=3

=>\(\left(a+1;b+2\right)\in\left\{\left(1;3\right);\left(3;1\right);\left(-1;-3\right);\left(-3;-1\right)\right\}\)

=>\(\left(a,b\right)\in\left\{\left(0;1\right);\left(2;-1\right);\left(-2;-5\right);\left(-4;-3\right)\right\}\)