If $\tan\dfrac{\alpha}{2}$ and $\tan\dfrac{\beta}{2}$ are the roots of the equation $9x^2-26x+15=0$ then $\cos(\alpha +\beta)$ is equal to?
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If $\tan\dfrac{\alpha}{2}$ and $\tan\dfrac{\beta}{2}$ are the roots of the equation $9x^2-26x+15=0$ then $\cos(\alpha +\beta)$ is equal to?