[tex]\displaystyle 1)x^2+3x-12=0\\D=3^2-4*1(-12)=57\\\\x=\frac{-3б\sqrt{57} }{2}\\ \\2)15x^2-7x-20=0\\D=(-7)^2-4*15(-20)=1249\\\\x=\frac{7б\sqrt{1249} }{30}\\ \\3)3x^2-5=0\\D=0^2-4*3(-5)=60\\\\x=\frac{б\sqrt{60} }{6}=\frac{б2\sqrt{15} }{6}\\ \\x=б\frac{\sqrt{15} }{3} \\\\4)13x^2+15x=0\\D=15^2-4*13*0=225\\\\x=\frac{-15б\sqrt{15^2} }{26}=\frac{-15б15}{26}\\ \\x_1=0,x_2=-\frac{15}{13}[/tex]
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[tex]\displaystyle 1)x^2+3x-12=0\\D=3^2-4*1(-12)=57\\\\x=\frac{-3б\sqrt{57} }{2}\\ \\2)15x^2-7x-20=0\\D=(-7)^2-4*15(-20)=1249\\\\x=\frac{7б\sqrt{1249} }{30}\\ \\3)3x^2-5=0\\D=0^2-4*3(-5)=60\\\\x=\frac{б\sqrt{60} }{6}=\frac{б2\sqrt{15} }{6}\\ \\x=б\frac{\sqrt{15} }{3} \\\\4)13x^2+15x=0\\D=15^2-4*13*0=225\\\\x=\frac{-15б\sqrt{15^2} }{26}=\frac{-15б15}{26}\\ \\x_1=0,x_2=-\frac{15}{13}[/tex]