1.
If the roots of the equation $$b{x^2} + cx + a = 0$$ be imaginary, then for all real values of $$x,$$ the expression $$3{b^2}{x^2} + 6bcx + 2{c^2}$$ is
Take the equation $$2a{x^3} + 3b{x^2} + 6cx = 0.$$ Clearly, $$x = 0, 1$$ are two roots. Observe that $$a{x^2} + bx + c = 0$$ is the derived equation. So, one root lies between 0 and 1.
3.
The real number $$k$$ for which the equation, $$2{x^3} + 3x + k = 0$$ has two distinct real roots in [0, 1]
$$\eqalign{
& f\left( x \right) = 2{x^3} + 3x + k \cr
& f'\left( x \right) = 6{x^2} + 3 > 0\,\,\,\,\,\,\,\,\,\,\,\,\,\,\forall \,x \in R\,\,\left( {\because \,\,{x^2} > 0} \right) \cr} $$
$$ \Rightarrow \,\,f\left( x \right)$$ is strictly increasing function
$$ \Rightarrow \,\,f\left( x \right) = 0$$ as only one real root, so two roots are not possible.
4.
The number of real solutions of the equation $$\sin \left( {{e^x}} \right) = {5^x} + {5^{ - x}}$$ is
Case 1 : $$x \geqslant 0$$
∴ the equation becomes $$x^2 + 5x + 4 =0$$ or $$x = - 1, - 4$$ but $$x \geqslant 0$$
∴ both values, non admissible : Case 2 : $$x \leqslant 0$$
The equation becomes $$x^2 - 5x + 4 = 0$$ or $$x = 1, 4$$ both values are non admissible
∴ No real roots. Alternatively, since $${x^2} \geqslant 0;\left| x \right| \geqslant 0$$
$$\eqalign{
& \therefore {x^2} + \left| x \right| + 4 > 0{\text{ for all }}x \in {\bf{R}} \cr
& \therefore {x^2} + \left| x \right| + 4 \ne 0{\text{ for any }}x \in {\bf{R}} \cr} $$
7.
If the roots of the equations $$px^2 + 2qx + r = 0$$ and $$q{x^2} - 2\sqrt {pr} x + q = 0$$ be real, then
As $$a\left( {b - c} \right) + b\left( {c - a} \right) + c\left( {a - b} \right) = 0,x = 1$$ is a root of the corresponding equation. The other root of the equation
$$ = \frac{{c\left( {a - b} \right)}}{{a\left( {b - c} \right)}} = 1$$ because $$a, b, c$$ in H.P. implies $$\frac{1}{b} - \frac{1}{a} = \frac{1}{c} - \frac{1}{b},\,{\text{i}}{\text{.e}}{\text{., }}\frac{{a - b}}{a} = \frac{{b - c}}{c}$$
∴ $$x = 1, 1$$ are the roots of the corresponding equation. So, $${\left( {x - 1} \right)^2}$$ is a factor.
9.
The number of real solutions of the equation $${2^{\frac{x}{2}}} + {\left( {\sqrt 2 + 1} \right)^x} = {\left( {5 + 2\sqrt 2 } \right)^{\frac{x}{2}}}$$ is