Bài 2: Tích vô hướng của hai vectơ

Trả lời câu hỏi Toán 10 Hình học Bài 2 trang 42 : Cho hai vectơ <svg style="display: inline-block; position: relative; top: -4px;" xmlns:xlink="http://www.w3.org/1999/xlink" width="2.324ex" height="3.009ex" viewBox="0 -1150.1 1000.5 1295.7" role="img" focusable="false" xmlns="http://www.w3.org/2000/svg" aria-labelledby="MathJax-SVG-1-Title"><title id="MathJax-SVG-1-Title">Equation</title><defs aria-hidden="true"><path stroke-width="1" id="E1-MJMATHI-61" d="M33 157Q33 258 109 349T280 441Q331 441 370 392Q386 422 416 422Q429 422 439 414T449 394Q449 381 412 234T374 68Q374 43 381 35T402 26Q411 27 422 35Q443 55 463 131Q469 151 473 152Q475 153 483 153H487Q506 153 506 144Q506 138 501 117T481 63T449 13Q436 0 417 -8Q409 -10 393 -10Q359 -10 336 5T306 36L300 51Q299 52 296 50Q294 48 292 46Q233 -10 172 -10Q117 -10 75 30T33 157ZM351 328Q351 334 346 350T323 385T277 405Q242 405 210 374T160 293Q131 214 119 129Q119 126 119 118T118 106Q118 61 136 44T179 26Q217 26 254 59T298 110Q300 114 325 217T351 328Z"></path><path stroke-width="1" id="E1-MJMAIN-20D7" d="M-123 694Q-123 702 -118 708T-103 714Q-93 714 -88 706T-80 687T-67 660T-40 633Q-29 626 -29 615Q-29 606 -36 600T-53 590T-83 571T-121 531Q-135 516 -143 516T-157 522T-163 536T-152 559T-129 584T-116 595H-287L-458 596Q-459 597 -461 599T-466 602T-469 607T-471 615Q-471 622 -458 635H-99Q-123 673 -123 694Z"></path><path stroke-width="1" id="E1-MJMAIN-2192" d="M56 237T56 250T70 270H835Q719 357 692 493Q692 494 692 496T691 499Q691 511 708 511H711Q720 511 723 510T729 506T732 497T735 481T743 456Q765 389 816 336T935 261Q944 258 944 250Q944 244 939 241T915 231T877 212Q836 186 806 152T761 85T740 35T732 4Q730 -6 727 -8T711 -11Q691 -11 691 0Q691 7 696 25Q728 151 835 230H70Q56 237 56 250Z"></path></defs><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="matrix(1 0 0 -1 0 0)" aria-hidden="true"> <use xlink:href="#E1-MJMATHI-61" x="235" y="0"></use> <use xlink:href="#E1-MJMAIN-2192" x="0" y="561"></use></g></svg> và <svg style="display: inline-block; 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position: relative; top: -4px;" xmlns:xlink="http://www.w3.org/1999/xlink" width="2.324ex" height="3.676ex" viewBox="0 -1437.2 1000.5 1582.7" role="img" focusable="false" xmlns="http://www.w3.org/2000/svg" aria-labelledby="MathJax-SVG-1-Title"><title id="MathJax-SVG-1-Title">Equation</title><defs aria-hidden="true"><path stroke-width="1" id="E1-MJMAIN-30" d="M96 585Q152 666 249 666Q297 666 345 640T423 548Q460 465 460 320Q460 165 417 83Q397 41 362 16T301 -15T250 -22Q224 -22 198 -16T137 16T82 83Q39 165 39 320Q39 494 96 585ZM321 597Q291 629 250 629Q208 629 178 597Q153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16Q290 16 318 46Q347 76 354 130T362 333Q362 478 354 524T321 597Z"></path><path stroke-width="1" id="E1-MJMAIN-20D7" d="M-123 694Q-123 702 -118 708T-103 714Q-93 714 -88 706T-80 687T-67 660T-40 633Q-29 626 -29 615Q-29 606 -36 600T-53 590T-83 571T-121 531Q-135 516 -143 516T-157 522T-163 536T-152 559T-129 584T-116 595H-287L-458 596Q-459 597 -461 599T-466 602T-469 607T-471 615Q-471 622 -458 635H-99Q-123 673 -123 694Z"></path><path stroke-width="1" id="E1-MJMAIN-2192" d="M56 237T56 250T70 270H835Q719 357 692 493Q692 494 692 496T691 499Q691 511 708 511H711Q720 511 723 510T729 506T732 497T735 481T743 456Q765 389 816 336T935 261Q944 258 944 250Q944 244 939 241T915 231T877 212Q836 186 806 152T761 85T740 35T732 4Q730 -6 727 -8T711 -11Q691 -11 691 0Q691 7 696 25Q728 151 835 230H70Q56 237 56 250Z"></path></defs><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="matrix(1 0 0 -1 0 0)" aria-hidden="true"> <use xlink:href="#E1-MJMAIN-30" x="250" y="0"></use> <use xlink:href="#E1-MJMAIN-2192" x="0" y="786"></use></g></svg> . Khi nào thì tích vô hướng của hai vectơ đó là số dương ? Là số âm ? Bằng 0 ?

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