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Question

Which of the following is a quadratic equation?

This question was previously asked in
RRB ALP 2018 CBT 2 Fitter Question Paper (21-Jan-2019) (Shift 3)
The correct answer is
$5x^2+4-7x$

Understanding Quadratic Equations

A quadratic equation is a polynomial equation where the highest power (degree) of the variable is 2. The standard form is \(ax^2 + bx + c = 0\), where \(a \neq 0\). We need to find the option where the variable '\(x\)' has a maximum exponent of 2.

Analyzing the Options

Let's examine each option to determine the highest power of '\(x\)':

  • Option 1: \(x^2+3x^3+5\)

    The highest power of '\(x\)' is 3 (from the term \(3x^3\)). This is a cubic equation, not quadratic.

  • Option 2: \(x^{3/5}+y^2-3\)

    This equation contains a fractional exponent (\(x^{3/5}\)). Quadratic equations must have integer exponents, specifically a highest exponent of 2.

  • Option 3: \(5x^2+4-7x\)

    The terms are \(5x^2\), $4$ (which is \(4x^0\)), and \(-7x\) (which is \(-7x^1\)). The highest power of '\(x\)' is 2. This equation can be written in standard form as \(5x^2 - 7x + 4 = 0\). Therefore, this is a quadratic equation.

  • Option 4: \(x^2-2x^{1/5}+2\)

    This equation includes a fractional exponent (\(x^{1/5}\)), disqualifying it as a quadratic equation.

  • Option 5:

    This option is empty and cannot be evaluated.

Identifying the Quadratic Equation

Based on the analysis, the only equation that meets the definition of a quadratic equation (highest power of \(x\) is 2) is Option 3.

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Important Questions from Quadratic Equations

  1. If the graph of a quadratic polynomial lies entirely above x-axis, then which one of the following is correct?

  2. If the roots of the equation x 2+ px + q = 0 are tan 19° and tan 26°, then which one of the following is correct?

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  4. If 2 + i is a root of the equation x 2- ax + 1 = 0, then the value of a is:

  5. If \(\tan \left( {\frac{α }{2}} \right)\)  and  \(\tan \left( {\frac{β }{2}} \right)\)  are the roots of the equation 8x 2- 26x + 15 = 0, then the value of cos (α + β) will be

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