[b]Resposta a)[/b] Parte fixa: 1200[br]Parte variável: 40 por hora [br]A função é[i] [b]f(x) = 40x + 1200[/b][br][br][/i][b]Resposta b) [br][/b]Sabemos que o total foi 1600, então:[br]40x+1200=1600[br]Resolvendo:[br]40x=1600−1200[br]40x=400[br]x=400/40[br]x=10[br]Logo, ele fez [b]10 horas extras[/b].

O zero acontece quando: [img width=57,height=18]data:image/png;base64,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[/img][br][br]Então:[br][br][left][img width=78,height=18]data:image/png;base64,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[/img][br]Resolvendo:[/left][img width=52,height=18]data:image/png;base64,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[/img][br][left][br][img width=43,height=34]data:image/png;base64,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[/img][/left][b][img width=35,height=18]data:image/png;base64,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[/img][/b][br][br][br][br]

A função dada é: f(x)=−3x+6[br]Comparando com a forma geral da função afim: f(x)=ax+b[br]Temos:[br][list][*]a=−3 (coeficiente angular)[/*][*]b=6 (coeficiente linear)[/*][/list] Analisando:[br][list][*]Como [b]a<0[/b], a função é [b]decrescente[/b][br][/*][*]Não é constante, pois a≠0.[br][/*][*]Não é linear do tipo f(x)=ax, pois b≠0[/*][/list]Conclusão: A função é [b]decrescente[/b], pois o coeficiente angular é negativo.