Resolucão:

Seja a função:

[tex]\qquad\qquad\large\tt{y=2x+3}[/tex]

Para determinar o valor numérico de y em função de x, basta substituir x pelos valores dados:

a) x=1/2

[tex]\qquad\qquad\large\tt{y=2\cdot \dfrac{1}{2}+3}\\\\\qquad\qquad\large\tt{y=\dfrac{2}{2}+3} \\\\\qquad\qquad\large\tt{y=1+3} \\\\\qquad\qquad\underline{\large\tt{\pink{y=4\checkmark}}}[/tex]

b) x=-2

[tex]\qquad\qquad\large\tt{y=2x+3}\\\\\qquad\qquad\large\tt{y=2\cdot (-2)+3}\\\\\qquad\qquad\large\tt{y=-4+3}\\\\\qquad\qquad\underline{\large\tt{\pink{y=-1\checkmark}}}[/tex]

c) x=0

[tex]\qquad\qquad\large\tt{y=2x+3}\\\\\qquad\qquad\large\tt{y=2\cdot 0+3}\\\\\qquad\qquad\large\tt{y=0+3}\\\\\qquad\qquad\underline{\large\tt{\pink{y=3\checkmark}}}[/tex]

[tex]\\[/tex]

Bons estudos! ◕ᴗ◕