1
JEE Main 2021 (Online) 20th July Evening Shift
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
Change Language
If sum of the first 21 terms of the series $${\log _{{9^{1/2}}}}x + {\log _{{9^{1/3}}}}x + {\log _{{9^{1/4}}}}x + .......$$, where x > 0 is 504, then x is equal to
A
243
B
9
C
7
D
81
2
JEE Main 2021 (Online) 20th July Evening Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
In a triangle ABC, if $$\left| {\overrightarrow {BC} } \right| = 3$$, $$\left| {\overrightarrow {CA} } \right| = 5$$ and $$\left| {\overrightarrow {BA} } \right| = 7$$, then the projection of the vector $$\overrightarrow {BA} $$ on $$\overrightarrow {BC} $$ is equal to :
A
$${{19} \over 2}$$
B
$${{13} \over 2}$$
C
$${{11} \over 2}$$
D
$${{15} \over 2}$$
3
JEE Main 2021 (Online) 20th July Evening Shift
Numerical
+4
-1
Out of Syllabus
Change Language
Let $$A = \{ {a_{ij}}\} $$ be a 3 $$\times$$ 3 matrix,

where $${a_{ij}} = \left\{ {\matrix{ {{{( - 1)}^{j - i}}} & {if} & {i < j,} \cr 2 & {if} & {i = j,} \cr {{{( - 1)}^{i + j}}} & {if} & {i > j} \cr } } \right.$$

then $$\det (3Adj(2{A^{ - 1}}))$$ is equal to _____________.
Your input ____
4
JEE Main 2021 (Online) 20th July Evening Shift
Numerical
+4
-1
Change Language
The number of solutions of the equation

$${\log _{(x + 1)}}(2{x^2} + 7x + 5) + {\log _{(2x + 5)}}{(x + 1)^2} - 4 = 0$$, x > 0, is :
Your input ____
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