Explanation
Consider the diagram shown above where QR represents the tree and PQ represents its shadow
Wehave,QR=PQLet∠QPR=θ" role="presentation" style="outline: none; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14.157px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; text-align: inherit; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; color: rgb(0, 0, 255);">Wehave,QR=PQLet∠QPR=θ
tanθ=QRPQ=1" role="presentation" style="outline: none; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14.157px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; text-align: inherit; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; color: rgb(0, 0, 255);">tanθ=QRPQ=1
(since QR = PQ)
⇒θ=45∘" role="presentation" style="outline: none; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14.157px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; text-align: inherit; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; color: rgb(0, 0, 255);">⇒θ=45∘
i.e., required angle of elevation = 45°