Question

Помогите пожалуйста , решить хоть что-то (

Answer 1

$B2)\; \; f(x)-nechetnaya\; \; \to \; \; f(-x)=-f(x)\\\\f(5)=-3\; \; \to \; \; f(-5)=-f(5)=-(-3)=3\\\\f(-2)=7\; \; \to \; \; f(2)=-f(-2)=-7\\\\f(5)\cdot f(-2)=3\cdot (-7)=-21$

$B4)\; \; \left \{ {{x-3y=3\; \; \; \; } \atop {x^2-9y^2=21}} \right.\; \; \left \{ {{x-3y=3\qquad \quad } \atop {(x-3y)(x+3y)=21}} \right.\; \; \left \{ {{x-3y=3\; \; \; \; \; \; } \atop {3\cdot (x+3y)=21}} \right.\; \left \{ {{x-3y=3} \atop {x+3y=7}} \right. \oplus \\\\\left \{ {{3y=x-3} \atop {2x=10}} \right.\; \; \left \{ {{y=\frac{2}{3}} \atop {x=5}} \right. \; \; \to \; \; (5,\frac{2}{3})\\\\2x+3y=2\cdot 5+3\cdot \frac{2}{3}=10+2=12$

$B5)\; \; 100<a<1000\; \; ,\; \; a=42\cdot x+x\\\\42\cdot 23+23=989\; \; ,\; \; 100<990<1000\; \; \to \\\\a=989$