Question

Determine as raízes reais das equações incompletas :

a) -x² + 12x = 0

b) 5 x² + x = 0

c) 25 x² -1 = 0

d)-7 x² + 28 = 0

ajudem plss​

Answer 1

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$\boxed{\begin{array}{l}\tt a)~\sf -x^2+12x=0\\\sf x(-x+12)=0\\\sf x=0\\\sf -x+12=0\\\sf x=12\\\sf S=\{0,12\}\\\tt b)~\sf5x^2+x=0\\\sf x\cdot(5x+1)=0\\\sf x=0\\\sf 5x+1=0\\\sf 5x=-1\\\sf x=-\dfrac{1}{5}\\\sf S=\bigg\{0,-\dfrac{1}{5}\bigg\}\\\tt c)~\sf 25x^2-1=0\\\sf 25x^2=1\\\sf x^2=\dfrac{1}{25}\\\sf x=\pm\sqrt{\dfrac{1}{25}}\\\sf x=\pm\dfrac{1}{5}\\\sf S=\bigg\{-\dfrac{1}{5},\dfrac{1}{5}\bigg\}\end{array}}$

$\Large\boxed{\begin{array}{l}\tt d)~\sf -7x^2+28=0\\\sf 7x^2=28\\\sf x^2=\dfrac{28}{7}\\\sf x^2=4\\\sf x=\pm\sqrt{4}\\\sf x=\pm2\\\sf S=\{-2,2\}\end{array}}$